Leaders of Pakistan's opposition on Tuesday urged the US to push for the restoration of democracy, warning that Washington risked an intensification of anti-American sentiment if it continued to back the military rule of President Pervez Musharraf.

The message, delivered against the backdrop of intensifying popular protests against Gen Musharraf, was targeted at Richard Boucher, US assistant secretary of state, ahead of his expected arrival in Islamabad on Tuesday evening.

"This is a defining moment in the history of this country," said Iqbal Zafar Jhagra, secretary-general of the Alliance for Restoration of Democracy, an umbrella organisation of Pakistan's mainstream opposition parties.

"When Boucher comes, the US must make a strong statement demanding the return of democracy. It's not possible for the US to continue justifying a uniformed president heading a democracy. It's a joke on democracy."

Although this week's searing heat, at times topping 50°C (122°F) in Lahore, has kept the crowds off the streets, the government remains shaken by the scale of recent protests against Gen Musharraf''s March 9 suspension of Iftikhar Chaudhary, the chief justice.

Analysts have warned that any signal from Washington of unconditional support could encourage Gen Musharraf to impose a state of emergency.

"Should this happen, Pakistanis would perceive the US as an impediment to, rather than a supporter of, democracy, and it would lose all remaining vestiges of credibility in the country," the International Crisis Group, an advocacy group, warned.

Pakistan's opposition parties have also been calling on the US to press Gen Musharraf to refrain from interference in the government's case against Mr Chaudhary, now being heard by the Supreme Court.

They urged Mr Boucher to call on Gen Musharraf to abandon his plan to have himself re-elected president by the existing parliament.

Condoleezza Rice, US secretary of state, last week said Washington was "encouraging [Gen Musharraf] to use the upcoming elections to make sure that they are done democratically, free and fair, that opposition is brought in."

Unless they agree to support Gen Musharraf, Nawaz Sharif and Benazir Bhutto, the exiled former prime ministers who lead the two largest political parties, face arrest if they try to return to Pakistan ahead of the parliamentary elections.

Since September 11 2001, western diplomats say the US's main priority has been to bolster Pakistan as an ally in the war on terror.

The shift in priorities has left the Bush administration open to charges of hypocrisy as it backs the Muslim world's most powerful military strongman in support of its goal of establishing democracies throughout the Islamic world.