New York authorities returned the alertness level to normal after haveing taken extra counterterrorism precautions over the weekend in response to what they said was an unsubstantiated radiological threat to the city reported by the Israeli Web site, DEBKAfile. DEBKAfile (www.debka.com) on Friday cited Internet chatter suggesting that al-Qaida would use trucks loaded with radioactive material or "dirty bombs" to attack New York. It also mentioned Los Angeles and Miami as possible targets for dirty bomb attacks. New York officials said that they had not changed the city's terror alert status in response to online chatter mentioning a truck packed with radioactive material. But police deployed extra radiological sensors on street, water and air patrols, and were stopping vehicles at checkpoints in lower Manhattan and around the city. Deputy Police Commissioner Paul J. Browne called the measures "strictly precautionary." He said DEBKAfile reported that online posts containing the terror warning were made following a video released Sunday featuring an American member of al-Qaida threatening foreign diplomats and embassies across the Islamic world. DEBKAfile's Giora Shamis defended the report, saying New Yorkers should be afraid. "There was definitely a sentence in the warning that referred specifically to New York," Shamis told Channel 10. DEBKAfile, a Web site founded in 2000 by Shamis and his wife, Diane Shalem, deals with security issues and is run out of Jerusalem. Security sources have sometimes questioned its credibility, saying some of its stories are conspiratorial and over-exaggerated. DEBKAfile refused to reveal the source of the dirty bomb report, but in response to a query from The Jerusalem Post as to whether the recent "chatter" constituted a genuine threat, an editor at DEBKAfile said that "DEBKAfile has been exposing al-Qaida's activities for eight years." "We have our sources, and [you can see] that the NYPD acted on our report," the editor said. New York's Daily News tabloid splashed the story on its front page on Saturday, with the headline, "Dirty bomb scare rocks city." "We are closely monitoring the situation," said Homeland Security Department spokesman Russ Knocke. "There continues to be no credible information telling us that there's a threat to the homeland at this time." The FBI also said there was no credible threat. Mayor Michael Bloomberg said the police measures were nothing out of the ordinary. "These actions are like those that the NYPD takes every day - precautions against potential but unconfirmed threats that may never materialize," he said in a statement.