Pakistan is embroiled in a political crisis less than six months after former army chief Pervez Musharraf was forced to resign as president by a civilian government that came to power in March last year.

Zardari, widower of assassinated former prime minister Benazir Bhutto, whose party leads a ruling coalition, is locked in a battle with former prime minister Nawaz Sharif.

Sharif's supporters have been protesting daily since last week when the Supreme Court barred Sharif and his brother from standing for election, and Zardari imposed central rule over Punjab province, dismissing its government led by Sharif's party.

Countrywide protests loom this month with Sharif's party and others backing a campaign organised by a lawyers' movement for the independence of the judiciary.

"If the situation is not arrested here, I see it getting worse," Sharif said in an interview as he drove through flat farm land to address a rally by thousands of supporters in the Punjab town of Narowal.

"His personal agenda comes into clash with Pakistan's agenda and with our agenda which is to restore democracy, restore the independence of the judiciary ... establish the rule of law."

Ostensibly, Zardari and Sharif, who head the country's two biggest political parties, disagree over the judiciary but at the heart of their feud is a struggle for power.

"BLUNDER"

Zardari's Pakistan People's Party won the most seats in an election in February last year and leads the federal government.

Sharif's party came second but won the most seats in Punjab, Pakistan's richest and politically most important province with more than half the members of the national parliament.

Whoever controls Punjab controls Pakistan, politicians say.

Two-time prime minister Sharif said there was no doubt Zardari was behind the Supreme Court ruling barring him and his brother from office though Zardari's party has denied that, saying it too wants an independent judiciary.

A year ago the two leaders were all smiles as Sharif joined Zardari's coalition. But a rift soon developed over the restoration of judges Musharraf had dismissed.

Sharif has committed his party to supporting a lawyers' movement trying to force Zardari to reinstate former Supreme Court chief Iftikhar Chaudhry who was suspended and later dismissed by Musharraf in 2007.

But Zardari fears if Chaudhry is reinstated, he could nullify an amnesty that Musharraf granted Bhutto and Zardari to enable them to return to Pakistan without fear of prosecution for old charges of corruption.

Sharif has won much support for his stand on the popular chief justice and while denying any thought of personal gain, he might in future need the help of judicial allies to clear hurdles to his return to power.

Sharif says last week's Supreme Court ruling has united Zardari's political and judicial opponents.

"Mr Zardari has made it possible, has linked the two together. This perhaps is one of his biggest blunders," he said.

The rivals' parties vied for power during the 1990s until the military stepped in. Analysts say if the situation deteriorates, the military might again feel it has to intervene.

The country, rescued by an IMF loan in November, can ill afford political turbulence as it struggles to get its economy on track and stem militant violence. Stocks fell again on Monday as the political crisis gnawed at investors.

"We have a very serious internal economic situation and this is not the way to give confidence to investors," Sharif said.