|Continuous attacks have prompted the US to urge Pakistan to do more to combat Islamist fighters [EPA]
Hillary Clinton has arrived in Islamabad on Friday in a surprise visit amid tense relations between the countries since the US raid that killed Osama bin Laden.
The US Secretary of State told Pakistani President Asif Ali Zardari and other officials that the US maintains "very strong support for the relationship and our commitment to working with and supporting Pakistan".
Clinton, who is accompanied by the chairman of the US Joint Chiefs of Staff, Admiral Mike Mullen, wants to soothe nerves and hurt feelings following the raid nearly a month ago by the US on bin Laden's compound.
A portion of the meeting briefly witnessed by reporters was stiff and awkward, with no smiles among the US delegation.
The discovery of the al-Qaeda leader in a garrison town just 50km away from Islamabad, Pakistan's capital, has raised doubts in the US about Pakistan being a reliable regional partner in the fight against the Taliban, both in Afghanistan and in Pakistan's border region.
The Pakistan government welcomed the death of Bin Laden but criticised the US secret mission in Abbottabad, where bin Laden allegedly lived for years, as a breach of its sovereignty.
"They have cooperated; we have always wanted more," a US official told reporters travelling on Clinton's plane ahead of the surprise visit.
"They have actually, from their perspective, done a lot. What they have never really grasped is how much more they have to do in order to protect themselves and, from our point of view, protect our interests and assist us in ways that are going to facilitate our transition in Afghanistan."
But many US politicians, sceptical that Pakistani officials did not know of bin Laden's presence, want to cut US aid to Pakistan, which the White House views as vital to counter-terrorism and to hopes of stabilising neighbouring Afghanistan.
In a sign of deepening distrust, Pakistan has told the United States to halve the number of military trainers stationed in the country.
Islamabad had asked for a scaling back of the US contingent of more than 200 troops earlier this month, Pentagon spokesman Dave Lapan said on Wednesday.
"We were recently notified in writing that the government of Pakistan wished for the US to reduce its footprint in Pakistan," he said. "Accordingly, we have begun those reductions."
He did not say how many troops would be pulled out. Most of the US personnel are special forces that train and advise Pakistani troops as part of efforts to counter al-Qaeda and other fighters.
Days after the raid on Bin Laden, Kayani, Pakistan's top soldier, said that any similar raid on Pakistani soil would prompt a review of military co-operation with the United States and informed army commanders of a decision to reduce the strength of US military personnel to "the minimum level".
However, just a day before coming to Pakistan, Clinton said working with Pakistan was a strategic necessity for the United States, even as she pressed Islamabad to act more decisively to counter terrorism.
She praised Pakistan as a "good partner" in global efforts to fight terrorism, though she acknowledged that the two countries had disagreed on how hard to fight al-Qaeda, Afghan Taliban fighters and other groups.
"We do have a set of expectations that we are looking for the Pakistani government to meet, but I want to underscore, in conclusion, that it is not as though they have been on the sidelines," she told a news conference in Paris on Thursday.
"They have been actively engaged in their own bitter fight with these terrorist extremists."