Police officials in New York responded by immediately tightening security at Israeli and Jewish facilities in the city.
In a dramatic change from its longstanding policy of not targeting the United States, Hamas issued an ominous statement claiming the U.S. gave its "consent" to Yassin's killing and saying the "terrorist American administration . . . must take responsibility for this crime."
"All the Muslims of the world will be honored to join in retaliation for this crime," the Hamas statement said.
A shadowy Al Qaeda (search)-linked group that claimed credit for the recent Madrid terror train bombings quickly heeded Hamas' call for revenge and vowed Muslims would strike "the tyrant of the age, America, and its allies," according to statement from the Abu Hafs al-Masri Brigades on an Islamic Web site.
American intelligence officials said they were concerned about the new statements from Hamas because they signal the group's previous hands-off posture toward the United States has now changed. "Anytime threats are made against the United States, we take them seriously," the U.S. official said, adding that American intelligence was closely watching the situation with Hamas.
Police Commissioner Ray Kelly told The Post that the terror group's threats are "something we have to be concerned about, and we have to be more vigilant in New York."
He said precinct patrols had been increased at the Israeli consulate, U.N. sites, Jewish temples and other potential targets.
Kelly said "no specific threats" had been received "but obviously that's not going to prevent us from doing things we have to do to protect the people of New York."
Israel felt the brunt of the first retaliation yesterday, with cross-border rocket attacks from Palestinians in the Gaza Strip and from Hezbollah in Lebanon, and the stabbing of three Israelis by an Arab on board a bus in Jaffa.
Sources in Jerusalem said the slaying of Yassin by three helicopter missiles was not an isolated event but part of a campaign launched last week to destroy the leadership of terrorist groups in the Gaza Strip.
Three other terrorist leaders - Yassin's top aides, Abed al-Aziz Rantisi and Mahmud A-Zahar, and the Islamic Jihad leader in Gaza, Abdullah Shami - are at the top of the target list, they said.
Prime Minister Ariel Sharon hinted at the ongoing assassination campaign yesterday when he said, "The war against terror has not ended and will continue day after day, everywhere."