Vice President Dick Cheney said on Sunday a new attack against the United States was ‘‘almost certain’’ as US Intelligence officials picked up signals that a fresh strike could be in the works. ‘‘In my opinion the prospects of a future attack against the United States are almost certain,’’ Cheney said on NBC’s ‘‘Meet the Press’’. ‘‘It’s not a matter of if but when,’’ he said. A US official said on Saturday that intelligence agencies had picked up ‘‘enhanced activity’’ suggesting Osama bin Laden’s al Qaeda network was planning a new strike. The New York Times said officials had intercepted a series of messages among al Qaeda operatives indicating the group is attempting an attack as big as or bigger than the one on Sept. 11, which killed around 3,000 people in New York, Washington, DC, and Pennsylvania. Cheney said the reports made it clear the threat was just as real now as it was last September. ‘‘We don’t know if it’s going to be tomorrow or next week or next year — partly because we’re having some success in disrupting the organisation and making it more difficult for them to carry out their operations,’’ he said. Cheney’s comments come as the White House has faced heavy criticism in recent days over disclosures that a series of possible clues about al Qaeda’s plans went unheeded in the months before the attacks. President George W. Bush has defended his handling of the intelligence ahead of the attacks, and Cheney said there was no information in the warnings that could have led to direct action to stop the attacks. ‘‘It’s almost impossible to erect a 100 per cent certain defense,’’ Cheney said.