Pakistan's Supreme Court ordered the release from prison on Tuesday of Ahmad Omar Saeed Sheikh, a ringleader in the kidnapping and murder of US journalist Daniel Pearl by al Qaeda and Pakistani Islamist militants in 2002.

Pakistan's government had appealed to the court on Friday to review its decision to free the British-born Islamist and three others convicted in the case, a day after their acquittal by a panel of three judges.

The United States also expressed concern over Sheikh's acquittal, and top U.S. diplomat Antony Blinken repeated a call for accountability in his first phone call with Pakistan's foreign minister on Friday.

The review panel, headed by Justice Omar Ata Bandyal, stood by the decision to acquit, and recommended that Sheikh should be moved to a "rest house" before being fully released.

"He should be moved to a comfortable residential environment something like a rest house where he can live a normal life," the judge said.

As the government makes the arrangements in next two days, Sheikh will be kept in a comfortable environment in the jail with a permission to see his family, the court said.

"It is not a complete freedom. It is a step toward freedom," the prisoner's father, Saeed Sheikh, told Reuters Television.

The terms of Sheikh's release will become clearer once a written order is made public.

On assignment for the Wall Street Journal in the months after al Qaeda 9/11 attacks on the United States, Pearl was kidnapped in Karachi and later beheaded. Al Qaeda's number three leader Khalid Sheikh Mohammed confessed to killing Pearl, and Sheikh, a former student at the London School of Economics, had played key role in luring the journalist into a trap.

Captured in Pakistan in 2003, Mohammed is being held at the U.S. detention centre at Guantanamo Bay, on the island of Cuba, where he is a awaiting trial on multiple counts, and could face the death penalty.