ATHENS, Greece - An antitank rocket slammed into the U.S. Embassy yesterday, causing limited damage and no injuries but reviving fears of a resurgence of far-left Greek extremist groups that carried out deadly attacks over three decades.

The shoulder-fired missile narrowly missed a large blue-and-white U.S. seal on the embassy's facade and damaged a third-floor bathroom near the ambassador's office.

U.S. Ambassador Charles Ries called the attack "very serious" and said no warning had been given.

"There can be no justification for such a senseless act of violence," he told reporters outside the cordoned-off embassy, which officials closed for the day. "The good news is no one was hurt and [there was] minimal damage."

Greek authorities blamed domestic groups that have carried out bombings against police and government buildings despite a crackdown before the Athens Olympics in 2004.

Police are examining the authenticity of two calls claiming responsibility from the group Revolutionary Struggle, which has carried out six bombings since 2003. The shadowy group has criticized the United States in past statements, citing treatment of prisoners at the U.S. military detention center at Guantanamo Bay, Cuba.

"It is very likely that this is the work of a domestic group," Public Order Minister Vyron Polydoras said. "We believe this effort to revive terrorism is deplorable and will not succeed."

State Department spokesman Sean McCormack said the United States also saw no early signs of international involvement. The Pentagon received a report on the attack but no request for any action, a U.S. military official said.

The blast shortly before 6 a.m. shattered windows in nearby buildings. Traffic in the downtown area came to a standstill for three hours as police blocked streets around the building to gather evidence - dusting cars for fingerprints and gathering discarded chewing gum and cigarette butts from the street.

The attack resembled methods used by members of the far-left group November 17, who eluded police between 1975 and eventual capture and conviction in 2003.

But the type of weapon used has not been seen in previous Greek attacks. Police identified it late yesterday as a 1.57-inch rocket-propelled grenade, RPG7, which was made in China in the 1970s from a Russian design.

Public opposition to U.S. policies - and the invasion of Iraq in particular - has remained strong in Greece since Washington provided support for a 1967-74 military dictatorship.

Government and opposition-party officials condemned the attack, the third against the U.S. Embassy since the mid-1970s.

Foreign Minister Dora Bakoyannis went to the scene, where she expressed "the solidarity of the Greek people following this deplorable action."

November 17 carried out a similar rocket attack against the embassy in 1996 - causing minor damage and no injuries. It also bombed buses carrying U.S. service personnel and assassinated four U.S. military and embassy officials. In all, the group was blamed for killing 23 people.