Greece, criticised by Washington over its anti-terrorism record, ordered a security alert at the U.S. embassy in Athens and other potential U.S. targets, including schools.

CNN: Attacks spark global red alert

The U.S. Customs Service said the added scrutiny is not an overreaction to threats of terrorism, but the result of following procedures during a heightened state of alert.

CNN: Ressam reportedly had ingredients for powerful chain reaction explosive