Intelligence officials in the United States apprehend a terrorist strike in the country in the next 30 to 60 days, Newsweek magazine reported quoting an 'internal' intelligence document.

Counter-terror analysts at the Central Intelligence Agency and the Federal Bureau of Investigation, the report said, were alarmed last week when they discovered a cryptic posting in the bulletin board of alsaha.com, an Abu Dhabi-based website.

"Oh brothers, further attacks are to come in the next 48 hours," it read. "All good Muslims in New York, Boston and other cities on the seacoast should leave."

The FBI and CIA, the report said, had no other direct warnings of an attack.

The terrorist 'chatter' level, the report added, is on the rise again. Electronic intercepts from tapped phones and spy satellites suggest that Al Qaeda operatives around the world were planning something. 

The federal authorities, it said, have identified a few Al Qaeda operatives already in the US and picked up one of them, who disclosed that he had been told to target a bridge and an airliner.