Islamabad  - Fears are growing that the Pakistani opposition's planned march on Islamabad this week might throw the nuclear-armed country into chaos and put the political future of pro-Western President Asif Ali Zardari at risk.

The political confrontation could also drive Pakistan away from its fight against extremism and efforts to overcome its economic crisis, two prime concerns Western governments want the Islamic country to focus upon.

An alliance of opposition parties, headed by two-time former prime minister Nawaz Sharif and the influential legal community, plans to start a protest rally, dubbed a long march, from the southern port city of Karachi Thursday and reach Islamabad four days later.

It plans to hold a sit-in in the capital until its demand for the restoration of the judiciary under independent-minded former chief justice Iftikhar Chaudhry is met.

The march was expected to swell in numbers as it travels through the eastern province of Punjab, Pakistan's most populace region and a stronghold of Sharif.

"It will have very dangerous dynamics for the country," said Rasool Bux Raees, a political science professor at the prestigious Lahore University of Management Sciences. "Violence, instability, protests, strikes and more confrontation will grow, and the government has not really realized the gravity of the situation."

Sharif's conservative Pakistan Muslim League-Nawaz joined Zardari's liberal Pakistan People's Party (PPP) in a coalition government after February 2008 elections, which saw the defeat of the political supporters of former military strongman Pervez Musharraf and the restoration of civilian rule after eight years.

But Sharif parted from Zardari after the president showed reluctance in fulfilling his promise of reinstating Chaudhry, who was sacked by Musharraf under emergency rule in late 2007.

The rift between the two widened last month when judges loyal to Zardari banned Sharif from elected office and nullified the election of his brother Shahbaz Sharif, suspending his provincial government in Punjab. Zardari said he did not dictate the verdict.

The February 25 court ruling triggered occasionally violent, countrywide protests and kept businesses closed for three days in Punjab, home to more than 60 per cent of Pakistan's 160 million people.

The concerns have grown in Washington and other Western capitals that the political infighting would divert Pakistan's attention from its fight against the Taliban and al-Qaeda militants launching cross-border attacks in Afghanistan.

British Foreign Secretary David Miliband said last week that the two leaders should put their differences aside and unite against the "mortal threat Pakistan faces," but the advice was not heeded by either side.

The efforts for mediation between the traditional opponents by US and British envoys also were unfruitful.

In a move that was likely to fail ahead of this week's march, the Pakistani government banned rallies in Punjab and arrested dozens of Sharif's supporters in a countrywide crackdown early Wednesday. Thousands of paramilitary troops were called in, and police were alerted to stop the protesters from entering the capital.

Pakistan's top security official, Rehman Malik, warned Sharif that his anti-government speeches are tantamount to sedition, which may be punished by a life sentence.

"Unfortunately, President Zardari and his loyalists have little political experience," Raees said. "They live in self-delusion that they can control the situation and suppress the opposition.

"Instead of finding the political means to resolve the issue, he is trying to block the rallies, but such attempts are unlikely to defeat the resolve of the seemingly charged opposition."

"And this is also going to put his own political future at stake," the professor added.

Zardari rose to power by chance after his wife, Benazir Bhutto, the former prime minister, was killed in a gun-and-bomb suicide attack during an election rally in late 2007. He became the head of her PPP and eventually the president.

But he has remained unpopular among the public for alleged corruption involving more than 1 billion US dollars during Bhutto's 1993-96 premiership.

Dissenting voices also emerged recently in his own party, challenging his decision to ignore senior party leaders and appoint inexperienced but loyal friends to key government posts.

The PPP's leader in the Senate and Bhutto's close aide, Raza Rabbani, resigned as a federal minister and Senator Enver Baig quit the chairmanship of the Senate's foreign affairs committee in protest over Zardari's nepotism, media reports said Tuesday.

There was also speculation about tensions escalating between Zardari and Prime Minister Yousuf Raza Gilani, also of the PPP. Gilani has occasionally resisted directives from Zardari, media reports said.

"From day one, Mr Zardari has tried to grab all powers for himself, and this has left him with few friends and many enemies," said the analyst and retired military general Talat Masood.

"It seems now that he has fallen in his own trap," Masood said, warning that if the crisis becomes acute, the country's military might intervene. "I don't see any future for him. Only a miracle will save him."

But Raees argued the military was unlikely to intercede. "Given the international scenario, the military is not in a position to take over as it has done in such political deadlocks in the past," the professor said.

"But if the political disorder grows further it might adopt a minus-Zardari formula that would amount to a removal of Zardari and bringing together all the political forces under certain parameters," he added. (dpa)