Pakistan's Supreme Court Thursday ordered the release of a British-born militant convicted of masterminding the kidnap and brutal murder of US journalist Daniel Pearl, who was beheaded by jihadists in 2002.

"The court has come out to say that there is no offence that he has committed in this case," Mahmood Sheikh, who represented the accused Ahmed Omar Saeed Sheikh, told AFP.

A court order released late Thursday said that Sheikh along with three accomplices connected to the case should "be released forthwith", though it was not clear when that would happen.

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

Nearly a month later, after a string of ransom demands were made, a graphic video showing his decapitation was given to officials.

Sheikh, a British-born 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.

He was later sentenced to death by hanging after telling a Karachi court that Pearl had already been killed days before the gruesome video of the journalist's beheading had been released.

Pearl's family on Thursday called the decision to free him "a travesty of justice" and pleaded for US intervention in the case.

"The release of these killers puts in danger journalists everywhere and the people of Pakistan. We urge the US government to take all necessary actions under the law to correct this injustice," the family said in a statement.

Reporters Without Borders also slammed the ruling, saying in a statement that it "will remain as a symbol of the absolute impunity surrounding crimes of violence against journalists in this country."

The ruling follows an international outcry last year when a lower court acquitted the 47-year-old Sheikh of murder and reduced his conviction to a lesser charge of kidnapping -- overturning his death sentence and ordering his release after almost two decades in prison.

That sparked a series of petitions against the acquittal, including from Pearl's family, but the Supreme Court rejected them in the split decision Thursday, upholding the acquittal.

'Travesty of justice'

For years Sheikh had denied personally killing Pearl, but the top court heard earlier this week that he had admitted to having had a "minor role" in a handwritten letter from 2019 that was sent to a provincial court.

Lawyers for Pearl's family have argued that Sheikh played a crucial role in organising the abduction and detention of the journalist, before ordering his captors to kill him.

Defence lawyers, however, say he was a scapegoat and sentenced on insufficient evidence.

Sheikh and the three other men convicted of involvement in the kidnapping have been held under emergency orders by the Sindh provincial government, which has argued that they are a danger to the public.

Late Thursday the Sindh government said it would file a review petition against the Supreme Court verdict. It was not clear how long that might take.

Last month the then-US acting Attorney General Jeffrey Rosen said Washington "stands ready to take custody of Omar Sheikh to stand trial here" after labelling the acquittal "an affront to terrorism victims everywhere".

In January 2011, following an investigation into the killing, a report released by the Pearl Project at Georgetown University made chilling revelations, claiming that the wrong men were convicted for Pearl's murder.

The investigation, led by Pearl's friend and former Wall Street Journal colleague Asra Nomani, and a Georgetown University professor, claimed the reporter was murdered by Khalid Sheikh Mohammed, the alleged mastermind of the September 11, 2001 attacks.

The report also provided granular details about Sheikh's alleged role in orchestrating the kidnapping of Pearl.