The United States is worried about the fate of Pakistan's nuclear weapons if President Pervez Musharraf [Images] is killed or overthrown while it feels the General may still impose a state of emergency despite ruling it out a couple of days ago, a media report said on Saturday.

American military intelligence officials, it said, are urgently assessing how secure the Pakistani nuclear weapons would be in that scenario -- if Musharraf is killed or overthrown.

Quoting three American sources, CNN reported that key questions in the assessment include who would control Pakistan's nuclear weapons after a shift in power.

It said that the three sources independently confirmed details of the intelligence review but would not allow their names to be used because of the sensitivity of the matter.

The United States is pressuring Musharraf, who came to power in a 1999 military coup, not to declare a state of emergency as he faces growing political opposition.

Although the Pakistani government ruled out the declaration of emergency on Thursday, the three sources told CNN the US thinks Musharraf may still impose those measures.

American analysts, the report said, are watching current Pakistani troop movements closely to see whether Musharraf is making any moves that could indicate he is about to impose emergency.

It appears that in recent weeks a large number of troops headed to the Pakistani tribal regions along the Afghan border, officials say.

Stating that the sources include military officers and intelligence community analysts, CNN said the assessment is part of a broader review of the military and security situation in Pakistan.

Unidentified officials were quoted as saying that Pakistan and its nuclear weapons are always a high intelligence priority for the US.

The current review is a result of recent developments in that country, including the prospect that Musharraf could still declare a national emergency that would give him sweeping powers.

Afghan officials, CNN noted, have accused Pakistan of allowing Taliban and al Qaeda fighters to regroup and carve out a new safe haven along Pakistan's largely lawless northwestern frontier.

The United States, the report said, has full knowledge about the location of Pakistan's nuclear weapons. But the key questions, officials say, are what would happen and who would control the weapons in the hours after any change in government in case Musharraf were killed or overthrown.

Musharraf controls the loyalty of the commanders and senior officials in charge of the nuclear programme, but those loyalties could shift at any point, officials were quoted as saying. The US is not certain who might start controlling nuclear launch codes and weapons if that shift in power were to happen.

There is also a growing understanding, according to the US analysis, that Musharraf's control over the military remains limited to certain top commanders and units, raising worries about whether he can maintain control over the long term, CNN said.

The US officials also say that one of the key problems for the American military is what restrictions on US-Pakistani military cooperation could be imposed if Musharraf were to impose heavy security restrictions in his country.