* U.S., Pakistan keen to revamp ties after years of tensions
* Both sides agree to restart strategic dialogue
* Kerry in Pakistan on an unofficial visit
* Tensions linger over use of U.S. drone strikes
The United States and Pakistan agreed on Thursday to re-establish a "full partnership", hoping to end years of acrimony over U.S. drone strikes on Pakistani soil, the raid that killed Osama bin Laden and other grievances.
"We are here to speak honestly with each other, openly about any gaps that may exist that we want to try to bridge," U.S. Secretary of State John Kerry said during an unannounced visit to Islamabad. "Our people deserve that we talk directly."
Besides the killing of bin Laden in a Pakistani town by U.S. Navy Seals in 2011, bilateral ties have also been severely strained by Pakistan's support for Taliban insurgents fighting Western troops in Afghanistan as well as a NATO air attack in which 24 Pakistani soldiers were killed.
Both sides are now keen to overcome the grievances and start afresh, a shift in priorities they hope is possible with a new government in Pakistan and a new secretary of state in the United States.
With Pakistan's economy badly in need of support and the United States keen on smoothly withdrawing most of its troops from neighbouring Afghanistan next year, both sides will see positives in repairing the relationship.
Speaking after talks with Prime Minister Nawaz Sharif in Islamabad, Kerry - who as a senator sponsored legislation to provide $7 billion in assistance to Pakistan over 5 years - said the two countries were serious about overcoming past irritants.
He invited Sharif to visit the United States - Pakistan's biggest donor - for talks with U.S. President Barack Obama.
"America does not want to have a transactional relationship, we do no want to have a relationship based on one moment or based on issues such as counter-terrorism or Afghanistan," Kerry said.
"What was important today was that there was a determination...to move this relationship to the full partnership that it ought to be, and to find the ways to deal with individual issues that have been irritants over the course of the past years."
He added: "And I believe that the Prime Minister is serious about doing that. And I know that President Obama is also."
Kerry, who arrived in Pakistan late on Wednesday, is the most senior U.S. official to visit Islamabad after Sharif's election in May.
Yet, continued U.S. drone strikes against militants in Pakistan's northwest remain a big hurdle. The use of drones is a highly sensitive issue in Pakistan and anti-U.S. feelings run deep in parts of the South Asian country.
Drone missiles have been hitting targets since 2004 in troubled areas on the Afghan border such as North Waziristan, the main stronghold for various militant groups aligned with al Qaeda and the Taliban.
Despite the tensions in ties, the United States remained Pakistan's biggest donor, although there have been calls in Congress in the past to cut off aid.
The ties improved fractionally last year after the two sides reached a deal to reopen land routes used to supply Western troops in Afghanistan that were cut off after the air strike in November 2011 that killed Pakistani soldiers.
Mutual suspicions however remain. Washington wants Islamabad to do more to eradicate militant havens and crack down on groups such as the Haqqani network which regularly attacks U.S. forces in Afghanistan from hideouts in Pakistan.
Pakistan itself has seen a spate of attacks against its military and civilians by the Pakistani wing of the Taliban since Sharif was sworn in on the back of promises to talk to the insurgents rather than fight them.
Speaking alongside Kerry, Sartaj Aziz, Sharif's adviser on foreign affairs, appeared to harden that position, saying his government might resort to the use of military force after all against the Taliban.
"Obviously dialogue has to go along with military action," he said, adding at the same time that Pakistan wanted the United States to end the drone strikes.
"We will explore that (talk) option first and if that doesn't work we will see under what conditions and by what time frame we do the alternative."
As for Afghanistan, Aziz and Kerry both expressed hopes to revive deadlocked talks with the Afghan Taliban as part of broader efforts to stabilise the nation as U.S.-led forces prepare to pull out most combat troops by late 2014.
Kabul has suspended talks on a security agreement with the United States after a dispute over how to proceed with the peace talks, prompting speculation the United States might opt for a "zero option" of withdrawing all troops after 2014.
Speaking about the future of U.S.-led forces there, Kerry said he was confident the United States would reach agreement on future troop levels in a timely way.
"We are drawing down, not withdrawing," he said. "I am personally confident we will have an agreement and the agreement will be timely."