The announcement did not elaborate as to who had sacked Sharif amidst reports of a coup by the armed forces and said Gen Musharraf would address the nation on television shortly.

Confirming the international community's worst fears, Pakistan is once again threatened by martial law as troops have occupied the official residence of Prime Minister Nawaz Sharif, taken control of the airport, State-run television and radio stations and placed key Government officials, including Information Minister Mushahid Hussain, under house arrest.

Unconfirmed reports said Sharif and his younger brother Shahbaz Sharif, Chief Minister of Punjab, are being held at the Prime Minister's residence in Islamabad. Reports from Lahore said Sharif's privateresidence in Lahore has also been occupied by troops.

Soldiers moved against the key installations following Sharif's announcement hours earlier that he had sacked Army Chief General Pervez Musharraf, who was on a visit to Sri Lanka but returned to Karachi Tuesday evening. By 11 pm, he was reported to be on his way to Islamabad.

Policemen guarding Sharif's official residence were disarmed and the Prime Minister was asked not to leave the building, unconfirmed reports said. Troops under the Rawalpindi Corps Commander, Lieutenant General Mohammed Aziz, surrounded Sharif's residence soon after radio and television announced that the powerful army chief had been replaced by Lt Gen Khwaja Ziauddin, head of the Inter Services Intelligence.

Army commanders outside Sharif's residence told PTI that the Prime Minister was inside the building. Journalists and Sharif's political colleagues were prevented from reaching his residence.

The new Army chief is also learnt to have been put under house arrest. Before itwent off the air, PTV had shown Sharif and Ziauddin clasping hands as his promotion to Army chief was announced. Sharif also dismissed the Chief of General Staff Mohammed Aziz, according to defence sources.

The troops also surrounded Islamabad international airport and entered the state-run radio and television buildings. The main PTV channel went blank around 7.30 pm (IST) after officials in the PTV headquarters told DPA about the presence of troops. It was followed by the stopping of broadcasts by Radio Pakistan. Mobile phones too stopped working after some time.

Soldiers have taken over the houses of several ministers, including Information Minister Mushahid Hussain, Foreign Minister Sartaj Aziz and Accountability Commission chief Saif-ur-Rehman. The governors' residences in Karachi and Peshawar have also been taken over by the Army.

Gen Musharraf, who returned from Colombo this afternoon, was reportedly given a ceremonial welcome by the Army at the Karachi airport. An AP report said he was met atthe airport by a large contingent of soldiers. He was seen leaving the airport accompanied by several jeeps filled with soldiers. He did not talk to reporters.

However, his daughter who had come to meet her father told reporters outside the airport that she tried to see him but was turned back. ``Don't you know it's a critical time, leave us alone,'' she told reporters while leaving the airport.

In Lahore, the home town of Sharif, soldiers in jeeps and trucks had taken positions on the main Mall Road and at government buildings.

There has been no word from either Sharif or the Army since Gen Musharraf's dismissal was announced. ``We don't know anything... Go to the Defence Ministry or to the Prime Minister's house. We also have heard like you (sic) on television,'' Colonel Salaut Raza of the Military Information Wing said.

No reason was given for Gen Musharraf's sacking, which the official APP news agency said took place ``with immediate effect'' late Tuesday afternoon. ``The Prime Minister hasretired General Pervez Musharaff, Chairman of Joint Chiefs of Staff Committee and Chief of the Army Staff with immediate effect,'' said the announcement.

The announcement gave no reason for the dramatic dismissal, which came only two weeks after Sharif had confirmed Gen Musharraf would complete his tenure as army chief and JCSC chairman on October 6, 2001.

A Special Services Group officer, Gen Musharraf was the second COAS to be forced out of office in as many years. The previous army chief, Gen Jehangir Karamat, was forced to resign last year following his differences with Sharif on the issue of setting up a national security council that would have given the army a greater role in administration.

There has been tension between Sharif and the military since the Prime Minister bowed to U.S. pressure and called for the withdrawal of Pakistani infiltrators, both troops and militants, from Kargil.

The new army chief was reported to be close to the Prime Minister as he had been hand-picked to head thesensitive ISI during a massive reshuffle in the army following the removal of Gen Karamat.