US-Pakistan ties "could not be more important", Secretary of State John Kerry has said, as he met Pakistani PM Nawaz Sharif in Washington.
Mr Sharif's three-day visit marks the highest-level talks between the two countries in the US for years.
The relations have been tense on several issues, including Islamabad's opposition to US drone strikes.
Meanwhile, President Barack Obama has asked Congress to resume $305m (£190m) in blocked security aid to Pakistan.
Washington's security assistance was interrupted following tensions in bilateral relations after a US commando raid on Osama bin Laden's compound in Pakistan in 2011 and the killing of more than 20 Pakistani soldiers in a US air strike.
'Challenge' to Pakistan
"We have a lot to talk about and the relationship with Pakistan could not be more important," Mr Kerry said before his meeting with Mr Sharif on Sunday.
America's top diplomat described Pakistan as "a democracy that is working hard to get its economy moving and deal with insurgency and also important to the regional stability".
Mr Sharif - who was elected in May - did not make public comments before the meeting started.
The talks are a strong sign of a willingness from both nations to co-operate, the BBC's Rajini Vaidyanathan in Washington reports.
Trade, dealing with extremism, and working on issues with Pakistan's neighbour, Afghanistan, were all set to be on the agenda, our correspondent says. So, too, was the thorny issue of US drone strikes.
Mr Sharif, who will meet President Obama on Wednesday, has said they are a challenge to his country, and that he will ask the US to bring an end to them.
The Pakistani PM earlier called for a joint strategy to stop such attacks.
The issue is highly controversial in Pakistan, where parts of the government and military have often been accused of criticising the use of drones in public while co-operating in private.
It is estimated that, between 2004 and 2013, CIA drone attacks in Pakistan killed up to 3,460 people - although this figure will not include the very latest strikes.
About 890 of those killed were civilians and the vast majority of strikes were carried out by the Obama administration, research by the Bureau of Investigative Journalism said.
Earlier this year, Mr Obama called the strikes part of a legitimate campaign against terrorism, but he also pledged more transparency in the programme and stricter targeting rules.