Prime Minister Yousuf Raza Gilani said on Sunday that the government could go to any length to assert the country's sovereignty, saying that “I do not rule out the closure of Pakistan's airspace to US planes”.

In an interview with the BBC, the prime minister also said the closure of routes for Nato convoys could continue for “a few weeks more”.

He said lifting of the suspension would have to wait until new terms of engagement with the United States had been agreed.

Mr Gilani admitted that there was a lack of trust between Pakistan and the US, which needed to be resolved.

“There is a credibility gap, we are working together and still we don't trust each other,” Mr Gilani said.

“I think we have to improve our relationship so that... we should have more confidence in each other.”

Asked whether he still believed that the Nato attack of Nov 26 were deliberate and pre-planned, Mr Gilani replied: “Apparently so.”

In reply to a question about President Asif Ali Zardari, he said medical tests were “clear” and he was improving.

He denied that the president had had a stroke or that he had written a letter of resignation, as claimed by a source in Dubai.

“Why should he write?” wondered Mr Gilani. “He has the backing and support of the entire parliament.”

“There was no stroke. 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.

Gilani also said he had talked with Zardari.

“He sounded very well. I did talk to him, and he has been talking to other ministers as well, to his son, to everybody,” he said, adding that the president had been exhausted, but was improving.

A cabinet member said earlier in the week that Zardari suffered a “minor heart attack” but a senior member of the Pakistan People's Party (PPP) clarified that the cause was “most likely a transient ischemic attack”, or minor stroke.

Medics say there is no lasting damage from a transient ischemic attack, but that it is an indicator of a possible stroke in the future.

He denied the army was trying to push the president out of office.

Mr Gilani dismissed speculations about a “quiet coup. “Rumours are rumours.”

BBC hails assurance

The BBC welcomed a promise by the prime minister to investigate the blocking of its World News channel in the country after it showed a documentary about the Taliban.

Cable operators pulled the channel nationwide on Nov 29 amid a row over the “Secret Pakistan” documentary and amid anger over the Nato air strikes.

In a statement issued in London, the BBC said Prime Minister Yousuf Raza Gilani had pledged in the interview with the broadcaster that he would “look into” the ban.

“We remain deeply concerned that BBC World News has been taken off air by the Cable Association of Pakistan,” a spokesman said.

“We welcome the prime minister's support of free speech and promise to investigate this ban. We call on the government to carry out an investigation rapidly and for BBC services to be restored in Pakistan.

“We condemn any action that threatens our editorial independence and prevents audiences from accessing our impartial international news service.”

Gilani said in the interview that his government supported media freedom and had abolished “draconian” laws from the past.

“And we have given freedom of media, and you are a witness here that how many channels are working day in and day out against the government. And if this is a specific which you have mentioned, I will look into it,” the BBC quoted him as saying.The two-part BBC documentary “Secret Pakistan” shown last month accused the country's intelligence services of complicity with Taliban.