Greek police are examining accounts from 10 people who witnessed an attack on the U.S. Embassy in Athens early Friday, state-run NET TV said Saturday.
Police said several witnesses saw three men and one woman - aged between 30 and 40 - fleeing on foot after a rocket-propelled grenade struck the facade of the embassy early Friday morning, NET said.
The attack caused limited damage and no injuries, but revived fears of a resurgence of far-left Greek militant groups that carried out deadly strikes over three decades.
The shoulder-fired missile damaged a third-floor bathroom and the blast shattered windows in nearby buildings, the AP wrote.
Forensic experts are examining fingerprints collected from the area around the compound as well as chewing gum and cigarette butts from the street.
Police are also investigating the authenticity of two calls claiming responsibility from the group Revolutionary Struggle, which has carried out six bombings since first appearing in 2003.
The group has criticized the United States in past statements, citing treatment of prisoners at the U.S. military detention center in 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."
In Washington, State Department spokesman Sean McCormack said the United States saw no early signs of international involvement, the AP said.
The weapon used in the attack has been identified as a Chinese-made RPG7 40-millimeter (1.57-inch) rocket-propelled grenade. It was made in about 1974 from a Russian design - a type of weapon never seen in previous Greek attacks.
The United States has imposed new sanctions against the Nord Stream 2 gas pipeline project, which still remains under construction