CIA warns Barack Obama that British terrorists are the biggest threat to the US Barack Obama has been warned by the CIA that British Islamist extremists are the greatest threat to US homeland security. By Tim Shipman in Washington 07 Feb 2009. The CIA has told President Barack Obama that British terrorists are the biggest threat to the US American spy chiefs have told the President that the CIA has launched a vast spying operation in the UK to prevent a repeat of the 9/11 attacks being launched from Britain. They believe that a British-born Pakistani extremist entering the US...