Arsonists have struck targets in the two largest U.S. cities, causing damage and raising concerns but resulting in no serious injuries.
In New York, authorities are investigating as possible bias crimes incidents that include a Molotov cocktail attack against a mosque in the borough of Queens.
Authorities say the device struck the door of the Imam Al-Khoei Foundation building Sunday as about 80 of its members gathered for dinner. The attack was one of a string of such incidents. A similar device also hit a convenience store shortly before the mosque was targeted.
Monday, police released a videotape of the attack and a sketch of a suspect, but no arrests have been made in the case.
Both the governor of New York, Andrew Cuomo, and the mayor, Michael Bloomberg, condemned the attacks. The governor said they "go against everything we stand for as New Yorkers and Americans."
Meanwhile, Los Angeles police on Monday arrested a man in connection with more than 50 arson fires that destroyed cars and buildings, causing at least $2 million in damage.
Harry Burkhart, 24, was arrested because he resembled a "person of interest" in the arsons.
Burkhart had been observed on a surveillance videotape near the Hollywood neighborhood where most of the attacks took place.
Los Angeles authorities point to a recent federal deportation hearing regarding Burkhart's mother as a possible motive in the case.
Despite having a suspect in custody, Los Angeles police officials encourage area residents to remain vigilant because it is an ongoing investigation.
Some information for this report was provided by AP, AFP and Reuters.