Unknown, pro-Palestinian activists set off a small explosive device outside offices in Piraeus where Israeli container liner company Zim is located.

Two gas canisters were used in the pre-dawn blast which caused slight material damage to a wall and a fuse panel, according to a police source.

Apart from Zim, the office building also houses the Greek branch of maritime security firm Diaplous Group.

Managers at both companies were not immediately available to comment.

However, police sources said the attack most likely targeted Zim and that its perpetrators were motivated by Israel’s war against the Palestinian Hamas group in Gaza.

Protest leaflets were found at the entrance of the building reading “Freedom for Palestine”.

Police detained some suspects who were later released, according to the state-run Athens News Agency (ANA).

Maritime assets owned by Israel or trading with the country are already the object of attacks at sea by the Houthi group, which controls large swathes of Yemen.

Attacks with home-made bombs are frequent in Greece. Often, they are politically motivated and carried out by militants and activists targeting state organisations, politicians’ homes and offices or companies with whose policies they disagree with.

Other attacks are the result of criminal disputes.

In a much more serious attack last month, a big explosive device went off in central Piraeus outside another office building that houses stores and shipping companies such as NorthStandard, Estoril Navigation, Primerose Shipping and Tototheo Maritime.

That explosion had demolished the building’s ground floor and smashed windows up to the second floor but did not seriously disrupt the companies’ operations.