Pakistan officials to 'finalise' end to Nato blockade
The Pakistani cabinet has ordered officials to finalise a deal as quickly as possible to bring an end to a six-month blockade on overland Nato supplies into Afghanistan.
But it has stopped short of announcing when the transit lines will reopen.
The US State Department said "considerable progress" had been made on ending the blockade.
It said it would work on getting it lifted before a key summit on the future of Afghanistan this weekend.
President Zardari is set to attend the summit, being held in Chicago.
The blockade of Nato's ground supply lines to Afghanistan was imposed in November, after a Nato air strike killed 24 soldiers.
The closure of the route left thousands of tankers bound for Afghanistan stranded in Pakistan.
Nato said that ending the blockade and attending the Chicago conference could give Pakistan a more concrete role in the future of Afghanistan as the alliance prepares to withdraw all combat troops from the country in 2014.
Pakistani Information Minister Qamar Zaman Kaira said after the cabinet meeting on Wednesday that there was no deadline for the blockade to be lifted.
"All departments have been asked to conclude their negotiations in the quickest possible time," he said.
Prime Minister Yousuf Raza Gilani said that relations with the US and Nato are "passing through a delicate stage, where we need to take critical decisions keeping in view of our strategic importance in the region and our national interest".
The cabinet welcomed Nato's invitation to President Zardari, clearing the way for him to attend the 20-21 May summit.
Correspondents say that the Pakistani government is likely to face an angry backlash over any decision to lift the blockade from opposition, right-wing and religious parties keen to exploit widespread anti-Americanism in an election year.
BBC correspondents say Pakistani leaders may have decided the blockade is counter-productive and has resulted in the country being sidelined in planning for Afghanistan's future.
Pakistan stayed away from the last major summit on Afghanistan, which was held in Bonn in December.
Pakistani lawmakers unanimously approved new guidelines for bilateral ties with the US in mid-April. They demanded that the US provide an "unconditional apology" for the November attack and stop drone strikes.
Correspondents say that although parliament did not explicitly link these issues to reopening the supply lines, matters have become more complicated because Washington has only expressed regret for the soldiers' deaths - stopping short of an outright apology - and continued with drone strikes.
Pakistani MPs also support the idea of Nato paying Islamabad a levy to use the routes, in addition to paying the lorry drivers' salaries.
The supply lines will become increasingly important as the 2014 deadline approaches, because Nato needs to withdraw huge amounts of equipment amassed over more than a decade in Afghanistan.
Correspondents say the US has recently reduced its reliance on Pakistan by using a more costly route through Central Asia.
The summit in Chicago on Sunday and Monday is said to be the largest meeting Nato has organised, with about 60 countries and organisations attending.