Police were seeking to determine the potential links of an Afghan national, arrested over the weekend, with a bagful of detonators, to Greek guerrilla groups.
The suspect, aged 30, was initially arrested on Saturday night after he tried to leave a restaurant without paying the bill.
Counter-terrorism officers took over the investigation once it was determined that the man had a rucksack with 78 detonators and gas canisters in his possession.
The bag also contained two bottles of butane, lighters, wicks and other items.
The suspect is to face a prosecutor as the police investigation continues.