Gilani, left, is under increasing pressure following his party's loss of its parliamentary majority [EPA]

The leader of Pakistan's main political opposition has given the ruling PPP a three-day ultimatum to agree to a series of reforms or face a possible no confidence vote.

Nawaz Sharif, who heads the Pakistan Muslim League-N party (PML-N), on Tuesday gave the PPP, or Pakistan People's Party, 72 hours to agree to reverse the fuel-price increase, cut government expenditures by 30 per cent, and implement a series of court verdicts against ruling party officials for corruption.

"If the government says no, if [Yousuf Raza Gilani] the prime minister says no, then we will ask the opposition parties to come forward and we will give them our full support," said Sharif during a news conference held in Islamabad after a meeting to determine the party's stance.

The demands also include setting up an accountability bureau to check corruption and tax collection, a PML-N spokesman told Al Jazeera.

He said the government would have until February 20 to show meaningful progress.

Analysts believe Gilani would probably try to keep Sharif on side because his party holds the second-largest number of seats in parliament and could prompt a snap election if it call for a vote of no-confidence.

Political struggle

Such a vote became a possibility on Sunday after the PPP lost its parliamentary majority with the departure of the Muttahida Qaumi Movement (MQM), its junior coalition partner, to the opposition benches.

The PML-N had earlier declined to say whether it would be prepared to call a no confidence vote.

"Our aim is not to overthrow this government, but if it collapses, it will collapse because of its own incompetence and bad governance," Sadiqul Farooq, a PML-N spokesman, said earlier.

But following a party meeting in Islamabad, Sharif made clear his party would go further.

He also warned the party would be willing to withdraw from the governing coalition it has with the  People's Party on a local level in central Punjab province if his demands were not met.

Further compounding the government's problems, just hours after Sharif's announcement, Salman Taseer, the Punjab's governor and a prominent PPP member, was assassinated at a market in Islamabad, reportedly by a member of his own security detail.

Dozens of the party's supporters took to the streets of Lahore, Punjab's provincial capital, burning tyres and blocking traffic to protest against the assassination.