New York City police increased security throughout Manhattan on Friday and at bridges and tunnels in response to what they called an "unverified radiological threat."
Officials said on Friday that they had not changed the city's "orange" 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 Browne called the measures "strictly precautionary."
He said an Israeli Web site reported that online posts were made following a video released last Sunday featuring a US member of al-Qaeda threatening foreign diplomats and embassies across the Islamic world.
"We are closely monitoring the situation," said US 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."
New York has remained on an orange alert -- the second highest such level, below red -- since the Sept. 11, 2001, attacks that destroyed the World Trade Center.
The FBI also said there was no credible threat.
New York Mayor Michael Bloomberg also sought to soothe New Yorkers.
"Earlier this evening, the NYPD [New York Police Department] began taking several public precautionary measures visible to New Yorkers to guard against an unverified threat that was found on the Internet," he said.
"These actions are like those that the NYPD takes every day -- precautions against potential but unconfirmed threats that may never materialize," Bloomberg said.
"As New Yorkers, we've gone about our lives even with the daily threat level at `orange' every day since September 11, 2001. That threat level has not changed because of this unverified threat, and we shouldn't let anyone terrorize us by spreading fear," he said.