Americans abroad warned of "increased likelihood" of ISIS attack

WASHINGTON -- The State Department is renewing its global terrorism alert for Americans traveling abroad, saying it sees a heightened risk of reprisal attacks from the by the Islamic State of Iraq and Syria (ISIS) and its supporters.

In a new "worldwide caution" issued on Friday, the department said terrorist groups continue to plot strikes against Americans and U.S. interests in Africa, Asia, Europe and the Middle East. It said authorities believe there is "an increased likelihood" of reprisal attacks from ISIS militants since the U.S. and its coalition partners launched military action against the group in Iraq and Syria.

The alert replaces an existing warning issued in April and also notes the growing threat of kidnapping perpetrated by terrorists.

While U.S. intelligence has not identified a specific threat from ISIS to the homeland, sources told CBS News correspondent Bob Orr that there are worries that the militant group could inspire retaliatory attacks in response to the American strikes in Syria.

One fear is that a lone wolf, who may not be on law enforcement's radar, could be motivated to act in the name of ISIS. That kind of threat is very difficult to detect.

The other worry is about those Americans and Western Europeans who have already joined the ISIS ranks -- the FBI is trying to track more than 100 Americans who have gone, or have tried to go to Syria. Some have been stopped and arrested. Others are under surveillance. The concern is there may be some radicalized Americans who have returned from the fight without our knowledge.