WASHINGTON, Nov 12: Authorities at the Greensville Correctional Center in Virginia are preparing to execute Mir Aimal Kasi on Thursday for the 1993 murders of two CIA employees after President George W. Bush rejected his mercy petition.

Kasi, 38, a Pakistani citizen, is to be executed by lethal injection.

The scheduled execution has put Washington on guard against possible revenge attacks by Islamist groups. On Nov 6, the State Department warned US citizens living abroad to be ready for revenge attacks.

Despite Bush’s rejection, tribal chiefs and religious authorities in Pakistan are urging Islamabad and Washington to intervene in the execution and to get Kasi’s sentence commuted to life imprisonment.

On Monday, Kasi’s relatives told reporters in Quetta that Bush had rejected the mercy petitions of his mother and Human Rights Commission of Pakistan for converting his death sentence into life imprisonment.

Kasi was sentenced to death in 1997 for killing two CIA employees — Frank Darling and Lensing Bennett — and injuring three others outside the agency headquarters in Langley, Va.

Kasi’s two brothers are in the United States, seeking legal recourse to delay the execution.

Pakistani authorities have tightened security around the country after a religious party — Jamiat Ulema-i-Islam — threatened to hold a countrywide protest if Kasi was executed.

On Monday, hundreds of JUI workers protested in cities across Pakistan, urging the Bush administration to pardon Kasi.

Despite Bush’s rejection of the mercy appeal, the chieftain of the Kasi tribe, Nawab Abdul Zahir Khan Kasi, once again appealed to the American president to pardon Kasi. “We are peaceful, law-abiding and civilized people and do not believe in violence,” Zahir Kasi said Monday, expressing regret over the killing of the CIA employees.

Aimal Kasi had returned to Pakistan after the 1993 slayings and had gone into hiding, but FBI agents and Pakistani security officials arrested him from the tribal belt of Dera Ghazi Khan on June 15, 1997. He was extradited to the United States.