Despite US-Greece relations being traditionally close, several hundred demonstrators poured onto the streets of Athens and Thessaloniki to protest against the visit of the US secretary of state.
In Athens, protesters occupied the main Syntagma Square, chanting "Americans, Murderers of Peoples", while playing music via loudspeakers, including in praise of famous revolutionary Ernesto "Che" Guevara.
One of the groups of protesters rallied outside the American Embassy, where they burned an American flag.
Another protest is being held in Thessaloniki, where people are expected to pass through Egnatia and Hagia Sophia Street to Tsimiski Street and stop at the US Consulate, before arriving at Venizelos Statue.
Amid the protests, the authorities have decided to to take emergency measures and have deployed some 1,000 police officers on the streets.