A Greek court on Monday handed prison terms to two Germans, a Frenchman and an Italian involved in an anti-mine protest that degenerated into attacks on police, local officials said.

The four men, part of anti-capitalist group Beyond Europe, each received an 18-month sentence but will likely be sent home, a judicial source said.

Nearly 80 protesters, mostly Germans, Britons, Italians and some Bulgarians, were rounded up on Sunday after allegedly throwing stones, bolts and other projectiles at riot police guarding the Canadian-operated goldmine expansion site on the northern Halkidiki peninsula.

The police fired back tear gas to disperse them.

Most of the detainees were released Monday but the four had refused to give their names to authorities.

On a bus where the protesters were cornered and caught, police said they had found slingshots, oxygen masks, hoods, fireproof gloves and scores of metal bolts.

Anti-mine protesters claim the Hellas Gold project, a subsidiary of Canada's Eldorado Gold, will cause irreversible harm to the environment, draining and contaminating local water reserves and filling the air with hazardous chemicals including lead, cadmium, arsenic and mercury.

The new goldmine on Skouries mountain has sparked years of protests, including a raid in 2013, when hooded militants threw Molotov cocktails at the mine worksite, wounding a guard and damaging equipment.

The Greek leftist government this week blocked work on the goldmine over alleged contract violations.

The energy ministry said the company had failed to provide an environment-friendly gold extraction plan within a three-year timeframe as promised, and had been given another year to deliver.

While in opposition, the now-ruling Syriza party publicly opposed the investment. However, many residents support the project.

Eldorado Gold, which already operates other mines in the area, this week said the suspension had put 5,000 direct and indirect jobs in Greece at risk.

Local miners on Monday briefly blocked roads in the area against the suspension of operations.