|The US and China have got behind regional rivals in the push for civilian nuclear power [Gallo/Getty]
Asif Ali Zardari, the president of Pakistan, has concluded his fifth visit to China since he came to power in 2008.
Amid much mutual backslapping and loud calls from the Pakistani president for more Chinese investment in his country's ravenous energy sector, Zardari and Hu Jintao, his Chinese counterpart, have stayed almost silent on the biggest of their shared concerns.
Neither side was expected to trumpet their blockbuster civilian nuclear agreement, which could knock another hole in the developing world's non-proliferation regime and lead Islamabad farther down the road away from Washington and towards Beijing.
The deal for China to design, build and finance two new nuclear reactors at an estimated cost of nearly $2bn has been out in the open for more than a year, but it is technically forbidden under international rules.
The US has offered only tame objections to the agreement, even though it sees a key ally in the fight against al-Qaeda and the Taliban moving closer to a competing world power.
"Five to six years from now, I think China-Pakistan relations will definitely outweigh US-Pakistan relations, especially because China is willing to invest in sectors outside the military," Rohit Honawar, a Pakistan analyst for the Mumbai-based Strategic Foresight Group, said.
Although many details have yet to emerge from last week's high-level meetings, the state-owned Associated Press of Pakistan reportedthat China's Three Gorges Dam Corporation has agreed to invest more than $100bn in hydro-electric projects in Pakistan.
Zardari has met dozens of corporate leaders from China's petroleum, aeronautic, banking and other sectors.
"Relationships between Pakistan and the US are definitely strong because of the war on terror," Honawar said.
"But what really matters are the ground perceptions of what people in Pakistan have of the US, and that at the moment is not in the US's favour."
The Pakistani media has played up Zardari's visit to China, and public awareness of the six-day trip to Islamabad's "all-weather friend" is "phenomenal", he said.
Meanwhile, only 17 per cent of Pakistanis recently surveyed by the Pew Research Centersaid they had a favourable view of the US.
"[T]here has been no attempt on China's part to secure an international consensus behind [the deal], nor to extract any concessions from Pakistan vis-a-vis proliferation issues"
Washington is hamstrung for a number of reasons when it comes to the impending nuclear deal, observers say.
Foremost is the unprecedented civilian nuclear pact the US made with India in 2005, which flew in the face of much of the previous international consensus and was viewed by many non-proliferation experts as a heavy blow to efforts to control the spread of nuclear technology.
Mark Fitzpatrick, a London-based nuclear policy expert with the International Institute for Strategic Studies, said the India deal "set a bad precedent".
Finally signed in 2008, the agreement required the US and India to negotiate an exemption from embargoes imposed by the Nuclear Suppliers Group (NSG), an international organisation that represents virtually all of the world's nuclear powers.
It also needed an unprecedented safeguards agreement from the International Atomic Energy Agency, the UN nuclear watchdog.
India and Pakistan, which both possess nuclear weapons, are the only countries, aside from Israel, that have not signed the Nuclear Non-Proliferation Treaty (NPT), and Pakistan warned prophetically in 2008 that the India-US deal would set a precedent for them.
The NSG rules prohibiting the sale of civilian nuclear technology to non-NPT states are voluntary, and there is no legal mechanism to punish countries that violate them.
"If China chooses to ignore them, there's not a whole lot that can be done," Fitzpatrick, a former US diplomat, said.
"The United States and other countries could apply diplomatic pressure ... [but] they may not be as vigorous in applying that pressure as would have been the case had the United States not committed the first sin of exempting India."
China has also worked with the US to contain Iran and North Korea's nuclear programmes, most recently voting in favour of a new round of UN Security Council sanctions against Tehran, a diplomatic coup for Washington.
Fitzpatrick, while allowing that there was no explicit evidence to support the theory, said some observers believe that China's assistance on Iran and North Korea was the basis of an "implicit quid pro quo" whereby the US would not seriously oppose Beijing's deal with Pakistan.
Indeed, the most recent reaction from the US state department was decidedly lukewarm.
P.J. Crowley, the department's spokesman, said in June that China needed to "clarify the details"of the deal and that it would require an exemption from the NSG similar to India's.
But analysts do not believe China is inclined to follow the same time-consuming US path before working with Pakistan - three years passed between a George Bush-Manmohan Singh news conference and the implementation of the India deal.
Pakistan's close relationship with China dates back decades, and Beijing has been largely responsible for the design, manufacture, financing and supply of Islamabad's nuclear infrastructure.
China helped build Pakistan's only two modern reactors, Chashma 1 and Chashma 2, located in the populous eastern province of Punjab.
In 2004, China joined the NSG, putting itself under the rules that forbid the sale and export of nuclear technology to Pakistan. But Beijing has argued that the new deal to build and supply Chashma 3 and 4 is consistent with the agreement for the first two and can be "grandfathered" into international acceptance.
"There is little appetite in Beijing for going through the sort of process that the United States undertook," Andrew Small, a China specialist with the German Marshall Fund of the United States, said in an interview with the Council on Foreign Relations.
"[T]here has been no attempt on China's part to secure an international consensus behind [the deal], nor to extract any concessions from Pakistan vis-a-vis proliferation issues."
The US is highly unlikely to play any role in Pakistan's nuclear power industry for the foreseeable future, in no small part due to concerns over Pakistan's record of poor nuclear stewardship.
Foremost were the dealings of Abdul Qadeer Khan, the father of the Pakistani government's nuclear programme, who confessed in 2004 to running a clandestine proliferation ring and supplying Iran, Libya and North Korea with nuclear weapons technology and expertise.
Two retired Pakistani nuclear scientists also travelled to Afghanistanin August 2001 to provide Osama bin Laden, the al-Qaeda leader, with advice on how to make nuclear weapons, according to media reports.
That history effectively blocks the US from having a hand in Pakistan's nuclear energy infrastructure, despite efforts to bolster ties between the two countries, including the multi-year, multi-billion dollar non-military aid bill signed into law in October.
It also opens the door to China, which has proven willing to deal with governments and in sectors the West finds more troublesome.
"It's impossible for the United States to be promoting civil nuclear energy co-operation with Pakistan the way China is, given the US leadership in the global non-proliferation regime and the concerns about the way that Pakistan's nuclear secrets were allowed to be sold for private gain to some of the world’s most dangerous regimes," Fitzpatrick said.
China's eagerness to proceed with the deal alarms non-proliferation experts like Fitzpatrick, who called Pakistan the "bete noire of the nuclear non-proliferation regime".
Moving forward will "clearly diminish" China's non-proliferation credentials, Peter Crail, a research analyst with the Washington DC-based Arms Control Association, said.
But Crail and Fitzpatrick, along with some Pakistani analysts, said they think it is a stretch to conclude that the nuclear deal is an indication of a developing rivalry between two powerful unions - India and the US versus Pakistan and China - even if relations between Islamabad and Beijing are rosy.
"China is Pakistan's largest defence equipment supplier. It is carrying out several projects in Pakistan. China and Pakistan are connected by the Karakorum Highway," Kamal Matinuddin, a retired Pakistani ambassador and army general, said.
"[The] Pakistani people consider China as an all weather friend unlike the USA."
Road to Kabul
But the US will not lose its influence in Pakistan, Matinuddin said.
"The road to Kabul leads through Islamabad, Obama knows that."
Jamshed Ayaz Khan, a retired Pakistani general and former president of the Institute of Regional Studies, said that Pakistan is well-placed in geostrategic terms and would be "a fool" to look in the "wrong direction".
He said he believes that the relationship between Pakistan and the US will improve when the Americans withdraw from Afghanistan.
Even as the US draws down its military presence next door, it is unlikely to simply pack up and leave, Fitzpatrick said.
"Given Pakistan's standing and size and role in the Islamic world, the United States needs to remain engaged in Pakistan and not let this kind of an axis [with China] form," he said.
That could be difficult, given China's rising influence in the region, growing economy, and strong desire to influence events in Pakistan.
Beijing in particular would like its neighbour to serve as a future energy route, according to Anatol Lieven, a professor at King's College in London and senior research fellow at the New America Foundation.
"China is very worried that its growing economy is far too dependent on sea-borne energy routes ... and that in any future conflict the Indian navy would find it very easy to block those sea routes," he said in an interview with Russia Today.
"China has been looking at a variety of different overland routes for energy from the Persian Gulf to flow to China, and one of those possibilities, actually it's becoming a reality, is to build an oil and gas pipeline across Pakistan, along the line of the existing Karakorum Highway across the Himalayas."
As China pushes the nuclear deal forward this summer, the prevailing wisdom is that the US will struggle to counterbalance its influence and Beijing will have its way.
Honawar said: "No-one wants to confront China."