Soldiers surrounded the residence of Prime Minister Nawaz Sharif, closed down the country's main airports and took over state radio and television.

The action followed the dismissal of Pakistan's army chief, General Pervez Musharraf, who is to address the nation shortly.

The BBC's Owen Bennett-Jones:"It's far from certain what General Musharraf intends to do now"

Troops are reported to have disarmed the police guard outside Mr Sharif's residence and the premier is believed to be inside the house.

The governments of the United States and India have expressed concern at the developments in Pakistan, and the Indian army has been placed on high alert.

And the governor of Pakistan's central bank has announced a bank holiday on Wednesday, apparently to arrest a massive outflow of foreign exchange from the country.

Army moves in

The army takeover began only minutes after General Musharraf was removed from his post.

The BBC's Brian Hanrahan: "The familiar scenario of a military coup began to play out"

He was on a visit to Sri Lanka when he was removed from office and was later reported to be at Karachi airport holding talks with senior military officers.

Mr Sharif appointed the head of the country's intelligence service, General Ziauddin, in his place.

Earlier state television went off air after soldiers scaled the gates of the building and took control.

Mr Sharif had been scheduled to visit the television studios.

Our Islamabad correspondent told BBC News Online that there is considerable confusion about who is behind the military action.

"It seems the army is not accepting this sacking and they may now be determined to take over .. which part of the army we don't know," he said.

"The electorate support the democratic government in Pakistan and opposition parties have stated that they would not back a military takeover."

Tensions with government

Former Pakistan Prime Minister, Benazir Bhutto, told the BBC that the army's action was a result of Mr Sharif's politicisation of the military.

Pakistan opposition leader, Benazir Bhutto: "A lot to do with Mr Sharif's running of the country"

She said some military officers loyal to Mr Sharif might offer pockets of resistance around the country.

No reason has been given for the decision to replace General Musharraf, who has just returned to Pakistan after a trip to Sri Lanka.

Earlier this month, the government said that the general had been confirmed as both the head of the army and chairman of the Joint Chiefs of Staff until 2001.

Ahmed Rashid of the Far East Economic Review: "It's a very confused situation"

However, there have been tensions between the government and General Musharraf ever since the Prime Minister, Nawaz Sharif, ordered the withdrawal of Pakistani-backed forces from the Indian side of the Line of Control in Kashmir in July.

The withdrawal came after the United States intervened to end some two months of fighting in the disputed territory.

Three weeks ago, a senior US State Department official said that Washington would oppose any attempt by political and military officials to overthrow the Pakistani government through extra-constitutional means.

The statement led to speculation that the army might be considering some move against the government.

Nawaz Sharif appointed General Musharaf last year when the former army chief, General Jehangir Karamat, stepped down after making remarks that were regarded as critical of Mr Sharif.

The BBC's Owen Bennett-Jones in Islamabad says the fact that the government of Nawaz Sharif has overseen the departure of two army chiefs within such a short space of time is likely to cause unease in the army.

The army has ruled Pakistan for 25 of its 52-year history.

If you live in Pakistan, we are interested to hear your experiences and accounts of the events in the country.