Pakistan's president, Pervez Musharraf, is facing the prospect of being thrown out of office after the country's fragile coalition government yesterday announced plans to impeach him.

The move plunged nuclear-armed Pakistan into fresh political turmoil, as it grapples to cope with a biting economic downturn and a security crisis that has seen Taliban-inspired militants take over its border region with Afghanistan and stage suicide bomb attacks across the country.

Musharraf is believed to have told supporters that he will fight the impeachment proceedings. He was plotting his response yesterday with advisers, and finally cancelled an on-off trip to the opening ceremony of the Olympic games.

"We elected him and now we will support him to defeat this move," said Kamil Ali Agha, a leader of the main pro-Musharraf party.

Pakistan's top military commanders also reportedly met yesterday, and the reaction of the army - which until recently was led by the president - is anxiously awaited by politicians and the public.

The breakthrough for the coalition, which has been able to agree on little since taking office four months ago, came after three days of talks between the Pakistan People's party, led by Asif Zardari, and Nawaz Sharif's Pakistan Muslim League-N.

"We want to make a new Pakistan," Zardari said at a press conference in Islamabad. "We have the votes and the political will."

To instigate an impeachment, the coalition must prove that the president has subverted the constitution or is guilty of gross misconduct. Musharraf's dismissal in November of the country's judiciary and suspension of the constitution for six weeks may form the basis of this.

However, impeachment requires a two-thirds majority in parliament, and the numbers are close. Musharraf's trump card may now be to use his power to dismiss parliament before it gets a chance to move the impeachment motion, under a constitutional mechanism that was used three times in the 90s to sack governments. If the president believes that the army is with him, he may be tempted to use this authority.

Impeachment has never been used in Pakistan before and there are fears that it could provoke another military intervention. "This decision was taken in haste. They are playing with fire," said Amin Fahim, an estranged senior member of the People's party. "Every action has a reaction."

The Pakistani military has indicated that it wishes to stay out of politics following Musharraf's decision to give up the job of army chief in November, when he clung on to his other role of president.

However, it is unclear whether the men in uniform, who have staged multiple coups over the course of Pakistan's turbulent history, will stand aside while a former army chief is humiliated and dragged out of office.

Sharif was thrown out of office by Musharraf in 1999, and many believe he is bent on revenge. Until now, Zardari has been much more reluctant to confront the president, procrastinating on the coalition's commitment to restore the judiciary.

"Impeachment is a device to distract attention from the restoration of the judges," said Iqbal Haider, a former law minister under Benazir Bhutto's government of the 90s.

But analysts said it would be difficult for Zardari to maintain credibility if he did not follow through with the impeachment threat.

"Our services to democracy are well documented," Zardari said. "I need no proof, no documentation from anyone ... the voice of the parliament is the demand of the people."

In the past, Musharraf has enjoyed strong support from Washington, as a major ally in the "war on terror"; the US has given Pakistan billions of dollars in military aid.

However, it now appears that the US may have given up on him. The White House said last night that impeachment was an "internal matter" for Pakistan.