WASHINGTON, Jan 20: The US government stepped up security across the country on Friday following the release of a new audiotape in which Osama bin Laden threatens to attack the US homeland.

The government, however, is not elevating the national alert level although Al Qaeda websites have posted new messages saying yet another tape is about to be released —- this one from Al Qaeda’s No. 2 man, Ayman al-Zawahiri. Zawahiri, who apparently escaped a missile attack that targeted him in Pakistan a week ago, will mourn his colleagues who were killed in that attack, the websites say.

The Osama tape, declared authentic by the CIA, was broadcast on Thursday by the Arabic news channel Al Jazeera. It was scratchy, and Osama’s voice sounded weak —- less robust than on his last audiotape a year ago.

But he minced no words in threatening the US with yet another major terrorist attack.

“The operations are under way,” he said in a translation of the tape, which was in Arabic. “And you will see them inside your own home as soon as they are finished, God willing.” In response to the new tape, Homeland Security officials are sending out a bulletin to 18,000 police agencies telling them to review all their intelligence. Local officials were being warned to pay attention to mass transit —- including subways, commuter trains and metro buses. Airports, water-treatment plants, chemical plants, and facilities storing radioactive material are also of concern.

Meanwhile, the White House has said that the threat will not deter the US from vigorously pursuing Osama and other top Al Qaeda leaders until they are either captured or killed. “We’re very much on the hunt against Al Qaeda’s senior leadership to keep them off balance,” said Jack Crouch, the deputy national security adviser.

Mr Crouch said there was no confirmation of reports by Pakistani officials that those killed in an air raid on a Bajaur village earlier this month included a top Al Qaeda bomb maker and a son-in-law of Ayman al-Zawahiri, Al Qaeda’s number two and the target of the strike.

Asked whether Zawahiri was among the dead, Mr Crouch said: “I don’t think there is a full understanding of that at this point.”

“It’s still ongoing, and we’ll have to determine in the future. And sometimes these things take time to determine,” he said.

Mr Crouch would not comment on the intelligence that led to the strike. But he said: “It’s important to reassure the American people that we are very much on the hunt against senior Al Qaeda leadership.” “Obviously, it is not only from the standpoint of bringing them to justice but also to make sure that if in fact they are planning any attacks on the United States and its allies that we try to interrupt those attacks,” he said.

“Our job is to put terrorists out of business and try to keep them from hurting Americans and hurting our friends and allies around the world,” he said.