ISLAMABAD (AFP) - Pakistani opposition politician Imran Khan's party announced Monday it is to renounce all its parliamentary seats, in a bitter row with the government over alleged poll rigging.

Former cricket star Khan claims last year's general election, in which his Pakistan Tehreek-e-Insaaf (PTI) party came third, was rigged and has demanded Prime Minister Nawaz Sharif resign and hold new polls.

The dramatic mass resignation came as the government tried to launch formal talks with Khan and populist cleric Tahir-ul-Qadri, who is leading a parallel protest, also calling for new elections.

Addressing his workers later in the evening, Khan said he would march on Islamabad's high-security "Red Zone" with his party workers and supporters on Tuesday.

"I will lead the march on the Red Zone and my workers will follow me," he told protesters, asking his party workers to remain peaceful during the march.

The heavily guarded Red Zone houses Pakistan's top government buildings and many foreign embassies.

Khan and Qadri on Saturday led thousands of supporters on a "long march" to the capital from the eastern city of Lahore, hoping to mobilise a mass movement to oust Sharif.

But Khan's protest failed to attract the vast crowds he had promised and other opposition parties on Monday shunned his call for a campaign of civil disobedience, leaving him looking increasingly isolated.

PTI vice-chairman Shah Mehmood Qureshi announced the shock mass resignation of MPs late on Monday afternoon.

"We are resigning from the National Assembly, Punjab Assembly, Baluchistan Assembly and Sindh Assembly," Qureshi told reporters.

He said the party was still making a decision about what to do in northwestern Khyber-Pakhtunkhwa province, where they are in power.

The MPs' resignations must be submitted to the national assembly speaker and passed on to the election commission.

Qureshi did not say when this would happen.

PTI scored their best-ever performance in last year's election, which Sharif won in a landslide victory and was rated as free and credible by international observers. They won 27 seats - which will now go to by-elections - and were awarded seven more through Pakistan's quota system for getting women and religious minorities into parliament.

Analyst Rahimullah Yusufzai said Khan had "isolated and weakened" himself with the civil disobedience call and the mass resignation was a risky gamble. "This is an act of desperation. It will not bring the government under pressure - it has already survived pressure of the march," he told AFP.

Before PTI's unexpected, high-stakes gamble, other opposition parties had distanced themselves from Khan's call for people to stop paying taxes and utility bills in protest against the government.

Former president Asif Ali Zardari, co-chairman of the Pakistan People's Party, the largest opposition party, said Khan's willingness to use "unconstitutional means" to pursue his goals threatened democracy.

"Democracy and nation will not be served by calls for civil disobedience nor by a stubborn refusal by any side to engage in a meaningful dialogue on political issues," Zardari said in a statement.

The authorities deployed tens of thousands of security personnel on Islamabad's streets and blocked main roads to contain the protests, but by Monday their numbers had ebbed and life was returning to normal.

There was more condemnation for Khan's civil disobedience call from the business community. The Federation of Pakistan Chambers of Commerce and Industry said the focus should be on getting the shaky economy back on track.

"Pakistan is in critical economic and political condition and political activities have hampered the process of economic and commercial development of the country," its president Zakaria Usman said in a statement.

A stinging editorial from Dawn, Pakistan's oldest English-language newspaper, said Khan had "miscalculated disastrously and painted himself and his party into a corner".

Sharif's Pakistan Muslim League-N (PML-N) has accused Khan of trying to derail Pakistan's perennially fragile democratic system. PML-N lawmaker and spokeswoman Marvi Memon said the government was not concerned by Khan's "ludicrous" civil disobedience appeal.

The nuclear-armed country has experienced three military coups and the latest crisis has triggered more speculation about possible intervention by the powerful armed forces.

ut sources said back-channel talks to resolve the row were under way on Monday and the government said it would soon announce cross-party committees to hold formal talks with PTI and Qadri.

Memon said the government wanted a negotiated end to the standoff but there was no question of Sharif resigning.

Last week the prime minister proposed a judicial commission to investigate election fraud allegations, but Khan immediately rejected the offer.

Qadri, a dual Pakistani-Canadian national, rejected the idea of talks with the government and said his deadline of midnight (1900 GMT) for the arrest of Sharif - over what he alleges was the murder of his supporters - still stood.

The cleric has said he will not be responsible for any repercussions if his various demands are not met.

Ten workers from Qadri's Pakistan Awami Tehreek movement were killed in clashes with police at his headquarters in Lahore on June 17.

A judicial commission was formed to investigate.