A police patrol on Thursday stopped a car carrying four passengers who had sledge-hammers and gas masks in the trunk of the vehicle. The car was stopped on the northbound lane of the national highway from Athens to Thessaloniki, which is hosting the annual international fair starting this weekend.
One of the four suspects had been arrested in 2014 for illegal weapons possession, while the other three are known by police as active anarchists, according to a report on Skai on Friday.
Police believe the four men to have been heading to the Thessaloniki International Fair (TIF), where they intended to engage in violent protest action expected from anti-establishment groups.
Dozens of protest rallies have also been organized by unions in the northern port, where Prime Minister Alexis Tsipras will be making the keynote speech on Saturday and outlining his government's policy plan for the year ahead.
Concerns about possible violence breaking out at some of these rallies has prompted the police to increase its presence in Thessaloniki, with more patrols and roadblocks.