Islamabad: Pakistan's government scrambled on Monday to survive after losing its majority, flinging the nuclear-armed state into a political crisis threatening to destabilise the US ally in the war on Al-Qaeda.

The decision by the Muttahida Qaumi Movement (MQM) to quit leaves Prime Minister Yousuf Raza Gilani's coalition hanging by a thread at a time of economic meltdown and heavy US pressure to do more to crack down on militants.

No civilian government in Pakistan has managed to complete a full term in office and with Gilani controlling around 160 seats in the 342-member national assembly, horse trading for new allies began immediately.

Although the prime minister is not bound to seek a vote of confidence in parliament, he could face serious problems in getting legislation passed and any failure to get the budget adopted in June could force snap elections.

Jamiat Ulema-e-Islam Fazl (JUIF), the prominent religious party that first shook the coalition by taking its seven lawmakers out of government in December after Gilani sacked one of its ministers, called again for his resignation.

"The prime minister has lost his majority. It's better for him now to resign with all his cabinet," its secretary general Abdul Ghafoor Haideri.

For the moment, Gilani has tried to appear calm, telling journalists: "The government is not going to fall."

Anti-government newspaper The News compared his optimism to British prime minister James Callaghan in 1979, shortly before he lost early elections, but most analysts believe the Pakistani government has time to play with.

Pakistan's powerful military establishment, which has ruled the country for more than half its existence, is widely reputed to not seek a political role under current army chief of staff Ashfaq Kayani.

President Asif Ali Zardari is chairman of the main ruling Pakistan People's Party and spokesman Farhatullah Babar told AFP that the presidency was still confident "that the problem will be solved and MQM's concerns addressed".

The MQM said its 25 lawmakers moved onto the opposition benches in protest at the government's nine percent increase in petroleum prices, inflation and record on corruption, but has left open the door to its future support.

"We'll support the government's positive steps while sitting in the opposition and will openly oppose the anti-people decisions," the party said.

MQM also remains a PPP coalition partner in the southern province of Sindh, of which Pakistan's largest city of Karachi is the capital and where the party's support is rooted in the Urdu-speaking majority.

Its dispute with the PPP has also been coloured by an explosion in political violence in Karachi, which one prominent PPP member blamed publicly on MQM supporters, and tax reforms demanded by the International Monetary Fund.

Pakistan has managed to stave off bankruptcy thanks to a 2008 IMF rescue package and after catastrophic flooding last summer, there are fears that Islamabad cannot meet key targets on inflation and budget deficit levels.

From the eastern city of Lahore, the Pakistan Muslim League Qaid-e-Azam (PML-Q), whose 50 lawmakers could prop up the government, said the prime minister had requested a meeting with party leader Chaudhry Shujaat Hussain.

"We haven't taken any decisions yet. When the prime minister comes, after that we will take a decision," Hussain told reporters.

Talks could stumble on the asking price for support and the need not to inflame the main opposition leader, former premier Nawaz Sharif, whose support would be needed for a vote of no-confidence to bring down the government.

Political analysts say the government's survival depends on how political parties react to the crisis, believing that few want to take on the mantle of Pakistan's myriad problems prematurely.

"If nobody presents a no-confidence motion, than legally there is no need for early elections and the present situation will continue," analyst Shafqat Mahmood told AFP.

"Morally the prime minister should take a vote of confidence but legally he is not bound. The government will face serious problems when it presents the budget. If the government fails to pass the budget then it will have to go."