ISLAMABAD: The Supreme Court on Thursday summoned Prime Minister Yousuf Raza Gilani to appear on February 13 to be indicted with contempt over his refusal to pursue corruption cases against the president.

The announcement significantly escalated pressure on the embattled prime minister, threatening to plunge his weak government deeper into crisis and force early elections within months.

Justice Nasir-ul-Mulk told the court that there were grounds to proceed against Gilani over the government's refusal to follow a court order and ask Swiss authorities to re-open corruption cases against President Asif Ali Zardari.

The government argued that Zardari had immunity from prosecution while head of state. Switzerland shelved the cases in 2008, when Zardari took office.

“We are satisfied that prima facie there is a case for further proceeding into the matter. Adjourned for February 13, for framing charges. Prime minister is required to remain present in the court,” Justice Nasir-ul-Mulk said in English.

The premier was previously summoned to appear in court on January 19, when he refused to back down on Zardari's immunity. Experts say that if convicted, he could be jailed for up to six months and disqualified from public office.

The prime minister’s lawyer, Aitzaz Ahsan, said it was possible to appeal.

“He (Gilani) has been asked to be present in person on February 13 when he will be indicted,” he said.

“There is a possibility for an appeal in this matter. It is up to the court whether to suspend this order or not. This will be decided after getting a copy of the order,” Ahsan added.

There was no immediate reaction Thursday from the prime minister or senior colleagues in the main ruling Pakistan People's Party.

Ahsan, hugely respected by judges for his role in forcing the government to reinstate independent judges in March 2009, has been presented as the best defence lawyer capable of finding a way of getting the prime minister off the hook.

But in some staggering exchanges in the court, the judges seemed determined to force the prime minister to write to the Swiss, although the Swiss themselves had said there was no case as long as Zardari was head of state.

“Suppose we discharge the (contempt) notice and withdraw the proceeding, what will you do? Will you write a letter or not?” Judge Sarmad Jalali asked Ahsan at one point.

Ahsan said that first the contempt notice had to be discharged.

“If you order writing the letter, it will be carried. But you have to decide on the contempt issue. I seek discharge of the notice on merit and I will not give any commitment on conditional discharge of the notice.”

Justice Asif Saeed Khosa also enquired why the letter had not been written.

“This is the court's order and there is clear direction from the court.”

Ahsan argued that the cases in Switzerland have been disposed off.

The allegations against Zardari were frozen by the National Reconciliation Ordinance (NRO), a political amnesty imposed in 2007, which the courts overturned in late 2009.

Tainted by corruption allegations, Zardari spent 11 years in jail on charges ranging from corruption to murder, although his supporters point out that he was never convicted.

Zardari and his late wife, prime minister Benazir Bhutto, were suspected of using Swiss bank accounts to launder about $12 million in alleged bribes paid by companies seeking customs inspection contracts in Pakistan in the 1990s.

A Swiss prosecutor has since said it would be “impossible” to reopen the case against Zardari since he benefits from immunity as a head of state.