U.S. authorities were investigating a credible terror threat surrounding the 10th anniversary of the 9/11 terrorist attacks, NBC News reported Thursday.

Members of the public react as they walk past a New York Police Department Hercules team on patrol near Penn Station in New York August 24, 2011. [Agencies]

"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.,"? CNN quoted a senior administration official as saying.?

The threat "has more credibility attached to it than the rest of the increasing chatter picked up in the past few days," NBC News?reported.?

Intelligence officials?said at least three individuals, including?an American, has?entered the country in August in an attempt to launch a "vehicle-borne attack against Washington D.C. or New York around the anniversary of 9/11."

It was believed that the suspected terrorists came from Afghanistan, and traveled through at least one other country, ABC News reported.

ABC News also?reported that U.S. law enforcement agencies are seeking at least two rental trucks nationwide. Those trucks were missing from locations in Kansas City, Missouri. It was not immediately known whether the search was connected to the plot.

White House officials said President Obama was briefed on the matter, and he had ordered federal agencies to boost security.

The U.S. is ramping up security measures?across the country as the 10th anniversary of the 9/11 attacks approaches.

"It's accurate that there is specific, credible but unconfirmed threat information," said Matthew Chandler, spokesman for the Department of Homeland Security. "As we always do before important dates like the anniversary of 9/11, we will undoubtedly get more reporting in the coming days. Sometimes this reporting is credible and warrants intense focus, other times it lacks credibility and is highly unlikely to be reflective of real plots under way."

"Regardless, we take all threat reporting seriously, and we have taken, and will continue to take all steps necessary to mitigate any threats that arise. We continue to ask the American people to remain vigilant as we head into the weekend," Chandler said in a prepared statement.

The White House said Wednesday that the administration is taking "all necessary steps" to guard against possible terror plots coinciding with the anniversary, as terrorists have shown interests in anniversaries in the past .

Earlier this month, Secretary of Homeland Security Janet Napolitano said the U.S. remains at "a heightened state of vigilance" and security measures are in place to detect and prevent plots against the United States.