The White House says a terror threat against New York and Washington remains credible but unconfirmed and President Barack Obama has no plans to change his plans to travel to ground zero.

Spokesman Jay Carney told reporters that Obama was briefed again about the threat Friday morning before heading to an economic event in Richmond, Va. The president told his top security advisers to ensure that all necessary precautions were being taken ahead of Sunday's 10th anniversary of the Sept. 11 terrorist attacks.

U.S. officials are pursuing what they call a credible but uncorroborated al-Qaida threat about a potential car bombing of bridges or tunnels in New York or Washington.

Obama is scheduled to mark the 9/11 anniversary Sunday at New York's ground zero, the Pentagon and Shanksville, Pa.