Five Greek men have been arrested by counter-terrorism police as part of a crackdown on far-right groups accused of attacking migrants and leftwing activists, Greek police said on Tuesday.

The five young suspects are accused of "participating in a criminal organization" and carrying out arson attacks and using explosives, officers said in a statement.

The police statement said eight houses have been searched in the greater Athens area and two provincial towns.

The statement also said officers confiscated Molotov cocktails, 50 kilograms of explosives, shotguns, knives, cudgels, drugs and far-right banners and paraphernalia.

The suspects are thought to be members of the Greek branch of the neo-Nazi Combat 18 group. Police said more residential searches are underway.

Combat 18 was a far-right group that began in Britain and later spread to other countries. The group's name is based on Adolf Hitler's initials -- the first and eighth letters of the alphabet.

Golden Dawn, a neo-Nazi party, remains the fourth largest in the Greek parliament.

A total of 70 Golden Dawn lawmakers and party officials are on trial on a wide range of charges, including membership of a criminal organization linked to the fatal stabbing of an anti-fascist rapper in 2013.

Far-right attacks have increased in Greece in recent months against leftwing activists and migrants.

In February, five people were injured after a group of eight people attacked an anti-fascist center in the Greek port of Piraeus.

The center was also attacked last August, and four people were arrested by the counter-terrorism unit in January.