By Syed Shoaib Hasan
BBC News, Islamabad
Pakistan's chief justice has told the head of the country's primary security agency to produce an illegally detained man or be sent to jail himself.
Judge Chaudhry is a staunch opponent of President Musharraf
The order against Tariq Pervez was made during a hearing into a "missing people" case in Islamabad on Monday.
Hundreds of people have gone missing in Pakistan since 2001.
Human rights agencies say that many are being illegally detained by the security agencies, which often deny any knowledge of their whereabouts.
"He must be produced today or you will be sent to the lock-up," Chief Justice Iftikhar Mohammad Chaudhry warned the director-general of the Federal Investigation Agency (FIA) Tariq Pervez.
Mr Chaudhry gave his order after hearing of the case of Hafiz Abdul Basit, who has been missing since 3 January 2004.
Some argue that the court is becoming more interventionist
His name is one of 287 missing people whose names appeared in a petition filed by their families and human rights organisations seeking their release.
The supreme court is now individually looking at each of the names and questioning officials as to their whereabouts.
Mr Basit was initially taken into custody by the police under unknown charges.
Mr Pervez, who was in the police at the time, was the officer responsible.
He told the court that Mr Basit was handed over to the Inter Services Intelligence (ISI) soon after his arrest.
Mr Pervez also said that he was unaware of the man's whereabouts and asked the court for a few days to find out.
Abuse of power
But Mr Chaudhry declined his request, and told Mr Pervez to produce the man within a few hours.
But he later allowed the director-general until Tuesday to produce Mr Basit.
The missing people's case came into the spotlight in late 2006, when Mr Chaudhry started regular hearings and ordered senior government officials to produce those in illegal detention.
Mr Chaudhry was suspended in March 2007 by President Pervez Musharraf on charges of abuse of power.
Gen Musharraf faces increasing unrest and opposition at home
But he was reinstated in July after the supreme court ruled the suspension to be illegal.
Since then, Mr Chaudhry has restarted his campaign of judicial activism, giving several anti-government judgements in political cases.
The court also ordered the immediate release of another missing man, Imran Munir.
The government says that he has been tried and court martialled for spying.
But a military appeal court is believed later to have declared a mis-trial, and his case is now under review.
His father told the court that Mr Munir was being detained as he had refused to marry the niece of a brigadier in the ISI.
Officials say Mr Munir has been brought to Islamabad and will appear in court on Tuesday.
"We will not adjourn this case till we have satisfactory answers," Mr Chaudhry said.