Hedayat Noor, right, father of Naeem Noor Khan with his lawyer Babar Awan after a hearing at a court in Rawalpindi (File photo - 14 Dec 2004)

Pakistani authorities say Mohammad Naeem Noor Khan was freed several days ago and is with his family in the southern city of Karachi.

Khan's lawyer, Babar Awan says the government gave no indication it had been considering the release.

"I was taken by surprise when I started arguing before the Supreme Court and suddenly the Attorney General came up and said Mr. Khan has been released," said Awan.

Khan was arrested in 2004 in the eastern city of Lahore.

Intelligence officers described Khan as a senior Al-Qaida computer expert.

He was seen as a liaison between the terrorist group's leaders and its militant forces around the world.

His computer contained alleged plans for possible terrorist attacks in London and several cities in the United States.

E-mails linked Khan to suspects in the 1998 U.S. embassy attacks in East Africa and led to a number of arrests in Africa, the Middle East and Great Britain.

Khan himself was reportedly never charged and officials familiar with his case say he cooperated with investigators who were leading a major sting operation targeting Al-Qaida militants.

His undercover work came to an abrupt end however after his name and detention were reported in the media only a few weeks after his arrest.

More recently Khan's name was tied to a separate and still unresolved controversy here in Pakistan.

Families and human rights workers have been pressing the government through the courts for information about several hundred suspected militants. They say the militants, including Khan, have been secretly and illegally detained as part of the government's war against terrorism.

The plight of the secretly detained has fueled opposition to the government's efforts to crack down on religious extremists.

At the same time U.S. officials say Pakistan has to do more to combat al-Qaida linked militants operating inside its borders.

Pakistan remains a key U.S. ally in the region although security experts say Al-Qaida is gaining ground in the country's remote tribal areas along the Afghan border.