Pakistan's President Asif Ali Zardari risks losing his immunity from prosecution, the country's supreme court has said in a contempt hearing against Yousuf Raza Gilani, the prime minister.
Gilani appeared in court on Thursday, facing contempt of court proceedings for failing to pursue corruption cases against the president.
Gilani had been summoned to explain his refusal to ask Switzerland to re-open fraud cases against Zardari dating back from 2003.
The prime minister told the court that Zardari could not be prosecuted as he was entitled to immunity.
"It is my conviction that he has complete immunity inside and outside the country," Gilani told judges. "In the constitution, there is complete immunity for the president. There is no doubt about that."
However, Al Jazeera's Imtiaz Tyab, reporting from the hearing, said the court then challenged the president's right to immunity.
"The court dropped a bit of a bombshell, that what if they don't recognise the immunity that is purportedly under the constitution?," he said.
Aitzaz Ahsan, Gilani's lawyer, contended that the issue under debate in the contempt of court case was not whether Zardari actually enjoyed immunity, but whether the prime minister believed that he did.
Hundreds of policemen were stationed outside the court in the heavily protected constitutional sector of Islamabad.
Several senior cabinet ministers and leaders of allied political parties attended the proceedings.
The next court hearing was set for February 1, and the court said the prime minister's legal representation could attend the session on his behalf.
In 2008, Swiss authorities shelved an investigation into alleged money laundering by Zardari and his late wife, Benazir Bhutto, a former prime minister who was assassinated in 2007.
The couple were suspected of using Swiss bank accounts to launder about $12m in alleged bribes paid by companies seeking customs inspection contracts in Pakistan in the 1990s.
The statute of limitations of the case expires in April.
The case was dropped by Swiss authorities at the request of the Pakistani government as part of an amnesty deal to heal the country's political problems.
But in 2009, the supreme court declared the amnesty unconstitutional, and ordered the government to re-open the case against Zardari. The government did not, and that is why Gilani has been accused of contempt.
The summoning of Gilani has plunged his government deeper into a crisis that could force early elections within months.
The government is also under immense pressure from the army and judiciary over an unsigned memo asking the US to prevent a feared coup last May.
Supreme court judges have six options on how to proceed which include finding Gilani in contempt, disqualifying the prime minister and president, and holding early elections.
Analysts say Gilani has to either resign or find a way of satisfying the court order if he wants to keep his job.
Some have suggested that the ruling Pakistan People's Party (PPP) could sacrifice Gilani to protect the president, who has been accused over the controversial memo that sought US assistance to curb the powerful military.
During the 1990s, Zardari had multiple cases of corruption, and even murder, lodged against him, all of which he says are false and politically motivated.
The National Reconciliation Ordinance (NRO), an amnesty deal that protected him and other political leaders, from prosecution was nullified in 2009 and the court has been pushing for the government to re-open and investigate the corruption cases against Zardari.
Musharraf delays return
In a separate development on Thursday, Pervez Musharraf, the former Pakistani president who is now the leader of an opposition political party, delayed his return to the country.
Musharraf, who has been living in Dubai and London since 2008, has been advised by aides to delay his return, citing concerns regarding his possible arrest.
Authorities in Pakistan say Musharraf is wanted over charges related to not providing Benazir Bhutto, Zardari's late wife and a former prime minister, with enough security on the day of her assassination in 2007.
"Party leaders are convinced it is not a suitable time for Musharraf to come to Pakistan," said Mohammad Ali Saif, central secretary in the retired general's All Pakistan Muslim League (APML).
Musharraf is due to make a final decision at a meeting of the party's leadership on January 25 and 26.