US Secretary of State John Kerry has held talks in Pakistan with newly-elected Prime Minister Nawaz Sharif.
The closed-door talks focused on the economy and security ahead of Nato's withdrawal from Afghanistan next year, officials said.Details of the negotiations will be made available later on Thursday.
Mr Kerry is expected to try to ease tension over controversial US drone strikes against suspected militants, correspondents say.
CIA strikes killed up to 3,460 people in Pakistan between 2004 and 2013.
The troubled border region of North Waziristan is considered an al-Qaeda and Taliban stronghold and US drones regularly target the area.
But Mr Sharif, who won elections in May, has demanded an end to such attacks, saying they violate his country's sovereignty.
Earlier this year, Mr Obama said the strikes were part of a legitimate campaign against terrorism, but he also pledged more transparency and stricter targeting rules.
'Historic transition' The US secretary of state is also expected to hold talks with Pakistani army chief Gen Ashfaq Kayani and President Ali Asif Zardari in Islamabad on Thursday.
It is Mr Kerry's first trip to
Pakistan as secretary of state, although he has a long history of
dealing with Pakistan as former chairman of the Senate Foreign Relations
Committee.
Before the pair began their talks Mr Sharif described him as
"a wonderful friend", while Mr Kerry replied that he "had the pleasure
of visiting Mr Sharif's home and having a number of meals with him''.The secretary of state paid tribute to Mr Sharif's victory at the polls. It marked the first time that an elected civilian Pakistani government completed a full term in office and handed over to another.
"This is a historic transition that just took place. Nobody should diminish it," he told US embassy staff.
"I think President Zardari deserves credit. It is historic. In the 66-year history of Pakistan that has never happened. So change comes over time," he added.
Correspondents say that relations between Pakistan and the US have recovered somewhat following the crisis sparked by the US killing of al-Qaeda leader Osama bin Laden in May 2011.
The economy, and Pakistan's energy shortages are also likely to discussed by Mr Kerry and Pakistan's new prime minister.
US officials travelling with Mr Kerry said Pakistan - although still formulating its counter-terrorism strategy following a spate of militant attacks - is likely to continue clampdowns on militants, but also engage them in talks.
The BBC's Kim Ghattas, in Islamabad says Washington wants to stress to Mr Sharif that extremism is a threat to both his own plans to strengthen the economy and a concern for the US, which has troops based in neighbouring Afghanistan.
The issue of drone strikes remains hugely controversial in Pakistan, where parts of the government and military have often been accused of criticising the use of drones in public, but co-operating in private.
Observers say Mr Kerry hopes to put a fresh focus on America's relations with Pakistan.
The last visit by a US secretary of state was in 2011, after al-Qaeda chief Osama Bin Laden was killed in a US raid in north-west Pakistan.
Ties between Washington and Islamabad were at breaking point then, our correspondent says.
But while the relationship remains difficult, it is considerably less tense now, partly because Pakistan's domestic politics have settled down