Terrorist group al Qaida was planning radioactive truck attacks on Los Angeles, New York and Miami, authorities confirmed a report on Sunday.

The planned attacks were revealed this week by Debka.com, an Israeli Web site that monitors terrorist activities. The website reported the threat based on "a rush of electronic chatter" on al Qaida Web sites.

According to the Israeli website, al Qaida communications accused America of not taking seriously last week's video narrated by al Qaida spokesman Adam Gaddahn, an American who grew up in Orange County, Southern California.

The video threatened terrorist attacks on American interests, especially embassies.

"They will soon realize their mistake when American cities are hit by quality operations," one message said.

Another message said the attacks would be carried out "by means of trucks loaded with radio-active material against American's biggest city and financial nerve center."

Debka reported that a third message mentioned New York, Los Angeles and Miami as targets.

The report said there was no way of gauging for sure how serious the threats were, or whether they were just mean to "give the Gaddahn tape extra mileage."

"But it is important to note that the exchange of messages took place over al Qaida's internal Internet sites and that they contained the threat of radioactive terror and specific American cities for the first time after a long silence on these subjects."

In response, authorities in New York City increased security and set up checkpoints to inspect vehicles.

But unlike authorities in New York, Los Angeles police had not beefed up security in response to the report.

In Los Angeles, the terrorist threat level was not raised and no increased security or extra patrols were ordered because the report was unverified, said Officer Mike Lopez of the Los Angeles Police Department's media relations office.

"We always hope to be prepared if anything should happen, but there is no special alert at this time," Lopez said.

Editor: Yan