Greek police said on Monday that the anti-terrorism unit was investigating what appeared to be a previously unknown guerrilla group after a group claimed responsibility for a bomb blast last week and another last year.
In a statement uploaded on the Athens Indymedia website on Sunday, the Revolutionary Class Self-Defense group said it carried out the April 11 explosion at railway operator Hellenic Train in response to a 2023 train crash that killed 57 people.
The explosion caused minor damage and no injuries. Police had evacuated the area after two media outlets received calls warning of the attack.