Hillary Clinton, the US secretary of state, has arrived at the Pakistani foreign office to chair a "strategic dialogue" between the two countries.
Clinton is expected to announce a major package of aid for Pakistan, totalling as much as $1.5bn, after several hours of discussions on Monday.
She met yesterday with Asif Ali Zardari, the Pakistani president, and Yousuf Raza Gilani, the prime minister, on the first day of her visit to Islamabad.
Clinton also attended a signing ceremony for an Afghan-Pakistan transit agreement, which will allow Afghan goods bound for India to travel through Pakistan.
Speaking before her meetings on Sunday, Clinton told the BBC news network that Washington and Islamabad had "increased our co-operation, deepened our relationship, when it comes to fighting terrorism".
However, she cautioned Pakistan's leaders had to do more to maintain the strong ties between the two governments in the face of potential security threats.
"There are still additional steps that we are asking and expecting the Pakistanis to take," Clinton said.
Tackling armed groups
The US delegation is expected to press Pakistan to escalate its war against armed groups in the country's northwest - particularly the so-called "Haqqani network" - supposedly the deadliest group operating in Afghanistan whose fighters often take sanctuary in Pakistan.
"For the United States, it is key that the Afghan government, and those Taliban elements who may join it, have no links to al-Qaeda"
Teresita Schaffer, an analyst at the US-based Center for Strategic and International Studies
Clinton will also likely press Pakistan on its role in "reconciliation" talks between anti-government fighters and the Afghan government. Some US officials suspect that Pakistan will encourage fighters with links to al-Qaeda to join the government.
"For the United States, it is key that the Afghan government, and those Taliban elements who may join it, have no links to al-Qaeda, and that Afghanistan does not again become a base for al-Qaeda," said Teresita Schaffer, an analyst at the US-based Center for Strategic and International Studies.
The Pakistani government, meanwhile, will have several requests of its own. The US pledged billions of dollars in development aid for Pakistan last year, but the two governments are still arguing over how to disburse that aid.
Pakistan's army also hopes to secure additional military assistance from the United States.
Shah Mehmood Qureshi, Pakistan's foreign minister, will meet Clinton on Monday for talks on the strategic dialogue started during his visit to Washington in March.
Since then 13 working groups covering topics ranging from development to defence have been set up to find areas for possible co-operation, and their progress will be reviewed by Clinton and Qureshi.
"The evolution of the strategic dialogue and the fact that we're delivering is producing a change in Pakistani attitude, first in the government, and gradually, more slowly in the public opinion," Richard Holbrooke, the US special representative for Pakistan and Afghanistan, said.
"This change is of strategic importance because it's enabling us to get to move forward on our additional efforts on counterterrorism and in terms of working together in the tribal areas."
Opinion polls suggest that fewer than one-in-five Pakistanis view the US favourably despite a tripling of civilian aid to $7.5bn in the next five years.
Shahed Sadullah, a Pakistan analyst, told Al Jazeera that the main puropse of the visit was to attempt to alter the perceptions of Washington in the minds of ordinary Pakistanis.
"Mrs Clinton is going to announce substantial development programmes in fields like energy and water and health, because it has been pointed out that you give Pakistan load of F-16s that is all very good, but the effect of that is not felt by the common man, the man on the street.
"It makes no difference to his life no matter how many F-16s you give to Pakistan. But if you have projects in these sectors, which are really problem in Pakistan, then you are doing things which can be felt by the common man and hopefully the image of US in Pakistan can be improved."
Clinton will travel to Kabul for an international donors' conference on Tuesday.