Washington, Sep 10 (IANS): US security head Friday asked all citizens to be vigilant against potential terror threat surrounding the 10th anniversary of the 9/ 11 terrorist attacks, Xinhua reported.

"As we head into the 9/11 anniversary weekend, we continue to urge the American public to be vigilant and report any suspicious activity to law enforcement authorities," US Homeland Security Secretary Janet Napolitano said in a statement.

Napolitano promised to take all threat reporting seriously, including the recent "specific, credible but unconfirmed" threat information disclosed by US officials Thursday night.

The position of Homeland Security Secretary was created by the US Homeland Security Act following the terrorist attacks of Sep 11, 2001. The secretary is a member of the President's Cabinet.

At least three individuals -- one believed to be a US citizen -- entered the country in August with the intent to launch a vehicle-borne attack against Washington D.C. or New York around the 9/11 anniversary, officials said.

"We continue to be in close contact with our federal, state and local law enforcement partners to ensure that all steps necessary to mitigate any threats are taken," Napolitano said.

White House press secretary Jay Carney said President Barack Obama was briefed Friday morning by his national security team, including the president's chief anti-terrorism advisor John Brennan, National Security Advisor Tom Donilon and his deputy Denis McDonough, on the threat.