It said that the US will continue to monitor any developments in the case and will continue to support the Pearl family 'through this extremely difficult process' while honouring the legacy of Pearl as a 'courageous journalist'

US State Department on Friday expressed "deep concern" over a Pakistani court's order to release British-born al-Qaeda leader Ahmed Omar Saeed Sheikh and his three aides, who were convicted and sentenced in the abduction and murder case of American journalist Daniel Pearl.

It said that the US will continue to monitor any developments in the case and will continue to support the Pearl family "through this extremely difficult process" while honouring the legacy of Pearl as a "courageous journalist".

A Pakistani court on Thursday ordered the immediate release of four men accused of orchestrating the 2002 kidnapping and murder of American journalist Daniel Pearl, including the main suspect earlier sentenced to death for masterminding the killing.

Sheikh, a seasoned jihadist who once studied at the London School of Economics and had been involved in previous kidnappings of foreigners, was arrested days after Pearl's abduction and later sentenced to death by hanging.

The decision by Sindh High Court to release the accused comes months after it sparked outrage for overturning the murder conviction and death sentence of Ahmed Omar Saeed Sheikh, and acquitted three other men connected to the case.

The four are being held under the emergency orders of the local government while an ongoing appeal against their acquittals is heard in the Supreme Court, but defence lawyers argued against their continued detention in the south of the country.

“All the petitioners ... shall be released from jail forthwith on the receipt of this order, unless they are wanted in any other custody case or any order against their release has been passed by the Honourable Supreme Court of Pakistan,” Thursday's court order read.

The April order has been challenged by the government at the Supreme Court, and Pearl's parents have also petitioned the country's highest judicial forum seeking the overturning of the decision to acquit the suspects.

Pearl was South Asia bureau chief for The Wall Street Journal when he was abducted in Karachi in January 2002 while researching a story about Islamist extremists.