20091227

WASHINGTON (Reuters) - There is no initial evidence that the Nigerian man charged with trying to blow up a U.S. passenger jet was involved in a larger plot, a senior U.S. official said on Sunday.

But al Qaeda involvement is a "subject of investigation" in Friday's incident, U.S. homeland security chief Janet Napolitano said after U.S. authorities on Saturday charged Umar Farouk Abdulmutallab, 23, with attempting to blow up the plane by setting alight an explosive device attached to his body.

The suspect, who was being treated for burns at a Michigan hospital, was overpowered by passengers and crew on the Northwest Airlines plane from Amsterdam on Christmas Day with almost 300 people on board.

"Well, right now we have no indication that it is part of anything larger. But obviously the investigation continues. And we have instituted more screening and what we call mitigation measures at airports," U.S. Secretary of Homeland Security Janet Napolitano told CNN's "State of the Union" program.

Asked whether al Qaeda was involved in the incident, Napolitano told ABC's "This Week" program, "That is now the subject of investigation, and it would be inappropriate for me to say and inappropriate to speculate. So we will let the FBI and the criminal justice system now do their work."

A senior U.S. official, speaking on condition of anonymity, said on Saturday authorities were looking at the possibility that Abdulmutallab had ties to al Qaeda in Yemen.

Abdulmutallab is due to make his first court appearance at 2 p.m. EST (1900 GMT) on Monday in federal court in Detroit on a motion from prosectors to take a sample of his DNA.

Napolitano said U.S. authorities were reviewing current rules on who goes on official watch lists used to identify people who might pose security threats and was reviewing screening policies and technologies.