ATHENS — Unidentified gunmen sprayed bullets into the headquarters of Greece’s governing New Democracy party in central Athens before dawn on Monday, adding to a wave of politically motivated violence in recent days as Greece struggles with its worst economic crisis in a decade.

No one was injured in the attack, in which one bullet entered the office of Prime Minister Antonis Samaras.

Though there was no public claim of responsibility for the shooting, the episode followed a spate of attacks on other symbols of the Greek establishment that are believed to have been carried out by far-left militant groups. Those attacks over the last week involved canister bombs detonated at several government offices, banks and the homes of five prominent journalists in Athens.

A government spokesman warned on Monday of a “dangerous escalation of spreading terror.”

Taken together, the episodes pointed to a rise in activism by far-left militant groups, after a similar rise over the past year on the far right, where the neofascist group Golden Dawn has carried out a series of attacks against immigrants.