Thousands of Greeks turned up at a rally and march in central Athens organised by the Communist Party to protest the US-led airstrikes against Syria.
The protesters gathered Saturday at Athens' central Syntagma Square before marching to the US Embassy, chanting anti-US slogans and carrying banners.
Some wrote on the pavement in red paint: "Americans, murderers of people."
Police vehicles barricaded access to the embassy and protesters left peacefully.
Dimitris Koutsoumbas, the Communist Party's leader, blasted Greek politicians for believing "flimsy excuses about a use of chemical weapons" by Syria.
He also criticized their "subservience" to the EU and NATO, as well as their support for Israel.
He told the crowd "the imperialists once again spill the blood of the local people. They destroy and splinter states by using fabricated evidence.