WASHINGTON - The United States said Friday it was unaware of a role by international terrorists in a rocket attack on the U.S. embassy in Greece, but cautioned that the investigation was still in its early stages.

State Department spokesman Sean McCormack said U.S. and Greek authorities were cooperating "to determine who's responsible for it and deal with them appropriately within the judicial system."

Greek authorities have said the attack was probably carried out by a domestic terrorist group.

When asked about that possibility, McCormack said: "We all know from history that there are a number of these anarchist groups in Greece, and that they are sometimes violent. I can't tell you if one of those is responsible for this particular attack."

Asked if there were any indications of international involvement in the attack, McCormack said "We're not aware of any, but, again, we're very early in the investigation."

A military official in Washington said there was no reason to believe that the attack was al-Qaida-related. The official is not authorized to speak on the subject and requested anonymity.

A U.S. intelligence official, who also spoke on condition of anonymity because the investigation was ongoing, said there was no information that suggests a follow-up attack.

The small anti-tank missile pierced the building above the front entrance early Friday morning. McCormack said nobody was injured and there was minimal damage.

The Greek foreign minister has visited the U.S. ambassador, McCormack said, and Secretary of State Condoleezza Rice called the ambassador for a briefing.

The embassy is set back 65 feet from the street, McCormack said, noting that the safety of U.S. embassies is "something that we take seriously."

Sad and scary at the same time.