Pakistan's blockade of the US supply line into Afghanistan, ordered in retaliation for a border strike, is likely to stay in place for weeks, Prime Minister Yousuf Raza Gilani has told the BBC.

Pakistan's fragile alliance with the United States crashed to new lows after November 26 when NATO air strikes killed 24 Pakistani soldiers in what the Pakistan military called a deliberate attack.

Gilani said in an interview with the BBC aired Sunday that the ban, already in its third week in the longest closure of the 10-year war, would not be lifted until new "rules of engagement" were agreed with Washington.

Asked whether that would be a matter of days or weeks, he replied: "weeks".

Gilani said there was still a "credibility gap" with the United States.

"We are working together and still we don't trust each other. I think we have to improve our relationship."

"We want to set new rules of engagement and cooperation with United States. We have a resolve to fight against terrorism and therefore we want to set new rules of engagement," he added.

Gilani stood by Pakistan's declaration that the border incident was a pre-planned attack, an allegation Washington rejects.

"Apparently yes and still there is an internal inquiry being conducted and we are waiting for the results," he said, adding that the motive for such a deliberate attack remained "a big question mark".

US President Barack Obama telephoned President Asif Ali Zardari to offer his condolences over the strike, but Washington has stopped short of apologising pending the outcome of a military probe due out on December 23.

Although Pakistani and US officials dispute the precise sequence of events, Pakistan closed its two crossings to US and NATO supplies and ordered American personnel to leave an air base reportedly used by CIA drones.

Pakistani-US relations, which have yet to recover from a secret American raid that killed Osama bin Laden on May 2, are considered at their lowest ebb.

In the interview, Gilani also said that Zardari has not suffered a stroke nor offered to resign despite rumours triggered when he flew to the United Arab Emirates for medical treatment a week ago.

Zardari fell ill in the midst of a major scandal over alleged attempts by a close aide to seek US help to limit the power of Pakistan's military.

"There was no stroke," Gilani said in the interview with BBC World News.

"He is improving and he is now out of ICU and he has been shifted to his room and I think he will take rest for about two weeks," he said.

Deadly attack on NATO convoy in Pakistan
Quetta, Pakistan (AFP) Dec 12, 2011 - Gunmen attacked NATO oil tankers stranded in southwest Pakistan for the second time in days as Islamabad warned it could enforce its blockade of the US lifeline into Afghanistan for weeks.

The attackers shot dead a driver and destroyed seven tankers in a blaze of fire late Sunday, the second attack in four days in Pakistan's volatile region of Baluchistan, rife with separatist and Taliban insurgency.

There was no claim of responsibility but Pakistan's fragile alliance with the United States crashed to new lows after November 26, when NATO air strikes killed 24 Pakistani soldiers in what Pakistan called a deliberate attack.

Islamabad sealed its Afghan border to NATO convoys, closures that entered an 17th day on Monday, forcing trucks back to the Arabian Sea port of Karachi.

Sunday's convoy was targeted in Dadar town, 90 kilometres (56 miles) southwest of Quetta, the capital of Baluchistan, police said.

"Around eight gunmen approached the convoy on motorcycles in Bolan district, ordered it to stop and started firing on the tankers," senior local police official Inayat Bugti told AFP.

"A driver of one of the tankers was also hit by a bullet and was killed instantly. The attackers later put the tankers on fire and escaped," he said.

Last Thursday, gunmen destroyed at least 34 trucks in a gun and rocket attack at a temporary NATO trucking terminal in Quetta.

The Taliban have in the past said they carried out such attacks to disrupt supplies for the 140,000 US-led international troops fighting in Afghanistan.

Prime Minister Yousuf Raza Gilani told the BBC that Pakistan's blockade of the border, already the longest since the 2001 US-led invasion of Afghanistan, will not be lifted until new "rules of engagement" were agreed with Washington.

"We are working together and still we don't trust each other. I think we have to improve our relationship."

"We want to set new rules of engagement and cooperation with United States. We have a resolve to fight against terrorism and therefore we want to set new rules of engagement," he added in the interview aired Sunday.

Despite the insistence from US commanders that the attack was not deliberate, Gilani stood by Pakistan's position that it was pre-planned.

US President Barack Obama telephoned President Asif Ali Zardari to offer his condolences over the strike, but Washington has stopped short of apologising pending the outcome of a military probe due out on December 23.

On Sunday, Pakistani officials said US personnel had left the Shamsi air base in Baluchistan, which they were ordered to vacate after the strikes.

The air base was widely reported to have been a hub for a covert CIA drone war targeting Taliban and Al-Qaeda fighters on Pakistani soil.

Pakistani-US relations have been in free fall this year, battered in January when a CIA contractor shot dead two men in Lahore and in May when US Navy SEALs killed Osama bin Laden near the capital without pre-informing Islamabad.