"We have received credible information very recently about a possible plot directed at the homeland that seems to be focused on New York and Washington, D.C.," a senior administration official said on September 8.

The official said the plot was believed to involve three individuals, including a US citizen. US officials believed the threat was a vehicle laden with explosives, but "the intelligence picture is not completely formed," the official said. "Not enough is known about the potential operatives and their plotting."

The threat is believed to entail a vehicle bomb, but "we cannot rule out other means," a US official said.

The information came in around noon of September 7, one official said.