The US has said it is ready to take custody of British-born al-Qaeda leader Ahmed Omar Saeed Sheikh, accused of kidnapping and murdering American journalist Daniel Pearl, asserting that Washington will not allow him to evade justice.

Acting US Attorney General Jeffrey A Rosen’s remarks comes days after a Pakistani court ordered release of Sheikh and his three aides, convicted and later acquitted in the kidnapping and murder case of Pearl.

“We cannot allow him to evade justice for his role in Daniel Pearl’s abduction and murder,” Rosen said on Tuesday.

Pearl, the 38-year-old South Asia bureau chief for The Wall Street Journal, was abducted and beheaded while he was in Pakistan investigating a story in 2002 on the links between the country's powerful spy agency ISI and al-Qaeda.

“We understand that Pakistani authorities are taking steps to ensure that Omar Sheikh remains in custody while the Supreme Court appeal seeking to reinstate his conviction continues,” Rosen said in a statement released by the US State Department.

“The separate judicial rulings reversing his conviction and ordering his release are an affront to terrorism victims everywhere,” he said.

We remain grateful for the Pakistani government's actions to appeal such rulings to ensure that he and his co-defendants are held accountable. If, however, those efforts do not succeed, the United States stands ready to take custody of Omar Sheikh to stand trial here," he said.

In a surprise move, a two-judge bench of the Sindh High Court last week directed security agencies not to keep Sheikh and other accused under “any sort of detention” and declared all notifications of the Sindh government related to their detention “null and void”. The court observed that the four men's detention was “illegal”.

Days later the Sindh province government said it has decided not to release Sheikh and his three aides in view of a Supreme Court’s September 28 order.

A three-judge apex court bench headed by Justice Mushir Alam, which is hearing the appeal by the Sindh government and the family of the slain journalist against the acquittal of Sheikh by the Sindh High Court in April, on September 28 noted that till the next date of hearing, the accused shall not be released.

A senior Pakistani government official said the apex court order has not been specifically recalled.

“The SHC in its December 24 order also clarified that accused should not be released if there is a Supreme Court restraining order regarding their detention,” the official added.

In April, a two-judge Sindh High Court bench commuted the death sentence of 46-year-old Sheikh to seven years imprisonment. The court also acquitted his three aides who were serving life terms in the case almost two decades after they were found guilty and jailed.

However, the Sindh government refused to release them and kept them in detention under the Maintenance of Public Order.

Their continuous detention was challenged in the Sindh High Court, which ordered their release on Thursday.

On Friday, the United States had expressed “deep concern” over the order to release Sheikh and his aides and said it will continue to monitor any developments in the case.

“We are deeply concerned by the reports of the December 24 ruling of Sindh High Court to release multiple terrorists responsible for the murder of Daniel Pearl. We have been assured that the accused have not been released at this time,” the US State Department said in a tweet.

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”.

The US has been mounting pressure on Pakistan, demanding justice for Pearl.

Pearl’s murder took place three years after Sheikh, along with Jaish-e-Mohammad chief Masood Azhar and Mushtaq Ahmed Zargar, was released by India in 1999 and given safe passage to Afghanistan in exchange for the nearly 150 passengers of hijacked Indian Airlines Flight 814.

He was serving a prison term in India for kidnappings of Western tourists in the country.