This file photo taken on June 19, 2001 of a TV grab of former Saudi citizen Osama bin Laden, from a video tape said to have been prepared and released by bin Laden himself, during shooting training at al-Faruq base in Afghanistan. Al-Qaeda mastermind Osama bin Laden was killed late on May 1, 2011 in a firefight with covert US forces deep inside Pakistan, prompting President Barack Obama to declare “justice has been done” a decade after the September 11 attacks. – AFP Photo

WASHINGTON: US Homeland Security Secretary Janet Napolitano said Monday she was not issuing, for now, a new terrorism alert after US forces killed Al-Qaeda leader Osama bin Laden in a raid in Pakistan.

“We remain at a heightened state of vigilance, but the Department of Homeland Security does not intend to issue an NTAS alert at this time,” Napolitano said, referring to the US National Terrorism Advisory System.

“I have been clear since announcing NTAS in January that we will only issue alerts when we have specific or credible information to convey to the American public,” she said in a statement.

US officials were worriedly watching for possible retaliation after special forces killed the Saudi-born militant in a hideout in Pakistan, nearly ten years after the September 11, 2001 attacks on the United States.

CIA director Leon Panetta warned Monday that terrorist groups “almost certainly” will try to avenge Osama bin Laden, the 9/11 mastermind killed in a raid in Pakistan by US commandos.

“The terrorists almost certainly will attempt to avenge him, and we must -- and will -- remain vigilant and resolute,” he said.

Napolitano said US officials “will continue to respond appropriately to protect the American people from an evolving threat picture both in the coming days and beyond.”

Napolitano had unveiled the NTAS in late April to replace the much-criticized color-coded US terrorism alert system, promising to provide more specific information and tell Americans what to look out for.