One of world’s top intelligence chiefs is warning that Al Qaeda militants in Syria are planning more attacks against the West.

MI5 Director-General Andrew Parker warned that the terror group is planning mass casualty attacks against the West, including the British transit system and iconic landmarks like Big Ben.

“We face a very serious level of threat that is complex to combat and unlikely to abate significantly for some time,” he said. “My sharpest concern as director general of MI5 is the growing gap between the increasingly challenging threat and the decreasing availability of capabilities to address it.”

Charlie Hebdo attack suspect Cherif Kouachi told a French television station before the takedown that he was sent by al Qaeda in Yemen. His brother Said reportedly trained with al Qaeda in Yemen back in 2011.

Officials are reviewing a claim of responsibility for the attacks by al Qaeda in Yemen.

Fox News has learned that the FBI and Homeland Security have sent out a joint intelligence bulletin to federal, state and local law enforcement, warning that the Paris massacre is a departure from recent lone wolf attacks because it showed evidence of training and premeditation.

The U.S. has also issued a worldwide travel alert.

Watch Catherine Herridge’s report above.