Anti-terrorism police, investigating a bomb threat, searched apartments at three buildings around the U.S. embassy in Athens Wednesday and briefly closed a busy road in front of the embassy building, authorities said.
Eleven people were being questioned by police after the search, but no explosives were found.
The Public Order Ministry said it had received information late Tuesday from a foreign national of a possible plan to attack the embassy.
A senior police official, who asked not to be named, told The Associated Press that all 11 people being questioned were Iraqi immigrants, and that the man who made the claim was also Iraqi.
Several roads behind the embassy building remained closed. Searches were being conducted in at least three buildings.
Police had originally told drivers in the area that the operation was an exercise.
Security around the embassy building in central Athens has been further heightened following a Jan. 12 attack on the embassy building with a rocket propelled grenade which caused no injuries.
A far-left Greek group, Revolutionary Struggle, later claimed responsibility for that attack, saying their action was in response to U.S. military involvement in Iraq, Afghanistan and Somalia.
Last month, the Greek and U.S. governments offered separate million-dollar rewards for information leading to prosecution of members of that domestic group.