WASHINGTON (CNN) -- Federal authorities on Thursday were preparing to launch a worldwide publicity campaign and offer a $2 million reward for helping officials locate a key suspect in the bombing of the U.S. Embassy in Nairobi, Kenya.

Federal law enforcement sources said a news conference would be held Thursday in New York to announce a criminal complaint against bombing suspect Abdallah Mohammed Fazul.

Fazul is believed to have played a central role in the blast at the embassy in Kenya.

Fazul, a native of the Comoro Islands, has been the subject of an FBI search for several weeks. He was believed to have fled to the United Arab Emirates.

"We don't know if he's in the U.A.E. or the Comoros, or where he is," a senior federal official told CNN. "If we did know where he was, we'd nab him," the official added.

The August 7 bombings at the U.S. embassies in the capitals of Kenya and Tanzania killed 257 people and wounded more than 5,000.