The court ordered Prime Minister Syed Yousuf Raza Gilani to appear in person before it on Thursday, Geo News reported.
"In these circumstances, we are left with no option, as a first step, to issue a show-cause notice," the court said.
A court panel had earlier threatened to dismiss Gilani if he did not reopen the cases against his boss, President Asif Ali Zardari, and several others as ordered by the court in 2009 after it struck down the National Reconciliation Ordinance amnesty agreement. The government has said Zardari has presidential immunity.
Gilani's civilian government, headed by Zardari, is facing court scrutiny while it remains locked in a standoff with the powerful military in a scandal arising from a memo in October.
The memo, which is also being investigated by the high court, alleged the Zardari government, through its ambassador Hussain Haqqani, sought U.S. help in averting a military coup in the country. Haqqani later resigned and is fighting his own legal battles.
The government has denied involvement in the memo scandal and sought to play it down.
Pakistan's army chief, Gen. Ashfaq Parvez Kayani, who dismissed rumors of a military coup, and the country's intelligence chief have insisted the high court investigate the memo.
Gilani has sought backing for his government from Parliament through a resolution in support of the political leadership for strengthening democracy and seeking the assembly's "full confidence and trust" in the leaders. That resolution was expected to be voted on Monday.
The fast-moving developments raised questions about whether the Zardari government can complete its term of office before the next elections, set for 2013.
The military is also upset over Gilani's dismissal last week of Defense Secretary Naeem Khalid Lodhi, a former general known to be close to Kayani. The dismissal was seen as an attempt by the government to assert control over the military.
On Sunday, Gilani said that under the Constitution he is answerable only to Parliament and not to any individual, the Pakistani newspaper Dawn reported.
He was reportedly answering a question on reports that Kayani had asked Zardari to ask Gilani to take back his remarks about the military chief.
The Los Angeles Times, quoting analysts, said the army is fed up with the Zardari government but is not looking for a military takeover, which could invite strong global criticism. The analysts said the military, instead, seems to be aligning itself with the Supreme Court, which has strong public support as well as legal authority to threaten the Zardari government.
In another development, Pakistani-American businessman Mansoor Ijaz, who reportedly made the memo public, did not appear Monday before a judicial panel looking into the scandal.
Pakistan's News International quoted Ijaz's lawyer Akram Sheikh as saying his client wanted more time to come to Pakistan.
Other reports quoted the lawyer as saying Ijaz would appear before the panel on or after Jan. 25 and that Ijaz was getting threats from certain quarters.
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