The U.S. Federal Bureau of Investigation (FBI) has warned law enforcement agencies of possible terrorism attacks if the "blind sheik," Egyptian cleric Omar Abdel-Rahmanwho, dies in U.S. custody, CNN reported Thursday.

Rahman, 68, had strong ties to al Qaeda and was seen as a key theological force behind the terror group, the CNN report said.

Rahman spat up blood on Dec. 6 in his prison cell in Missouri, and was rushed to a hospital, the FBI notice was cited as saying.

He was given blood transfusions at St. John's Regional Health Center in Springfield, Missouri, and a tumor was reportedly found on his liver. Rahman, who was serving a life sentence, was returned to prison after the treatment.

Rahman had been imprisoned since 1995 for inspiring the 1993 World Trade Center attack and a thwarted plot to attack bridges and tunnels, an FBI building, and the United Nations headquarters in New York, the report said.

He had called for revenge if he dies in jail.

There was no intelligence to suggest there were any attacks being planned, and the FBI bulletin was intended to alert all those in law enforcement of the possibility of a threat, according to the report.

Source: Xinhua