DETROIT, Dec 15 (Reuters) - The Nigerian man accused of trying to blow up a U.S. airliner with a bomb hidden in his underwear had gone to Yemen and received help in planning his attack, federal prosecutors said on Wednesday.
Umar Farouk Abdulmutallab was charged with a new count of conspiracy to commit terrorism in addition to the six previous counts related to attempted murder and carrying a bomb on a crowded passenger jet.
Abdulmutallab will be arraigned on the new charge, which carries a maximum life sentence, on Thursday in federal court in Detroit.
A superseding indictment returned by the grand jury in the case on Wednesday said there was evidence Abdulmutallab had traveled to Yemen in August 2009 to become involved in a "violent 'jihad' on behalf of al Qaeda."
Abdulmutallab "and others whose names are both known and unknown to the grand jury, conspired to engage in an act of terrorism transcending national borders," it said.
None of the other alleged conspirators was named.
Abdulmutallab, originally from Nigeria, boarded a Northwest Airlines flight from Amsterdam to Detroit and near the end of the trip on Dec. 25, he tried to ignite a bomb sewn into his underwear, prosecutors have said.
The explosives failed to detonate fully and Abdulmutallab was subdued by passengers and crew as the jet flew over Woodhaven, Michigan.
Abdulmutallab had been cooperating with U.S. investigators earlier this year and told them he received the device and training from al Qaeda militants in Yemen, U.S. officials have said.
The failed attack led to further efforts by the Obama administration to strengthen U.S. airline security.
Al Qaeda's Yemen-based branch is a serious threat to the United States and has become substantially more dangerous over the past two years, the top U.S. military officer said last month.
The group claimed responsibility for a recent foiled plot to send explosive parcels to the United States and for the crash of a UPS jet in Dubai in September. (Reporting by Kevin Krolicki; Editing by Peter Cooney)