A homemade device exploded in front of a church in central Athens on Thursday, injuring its caretaker and a police officer, police said.
The device was placed outside the Orthodox Church of Saint Dionysius in the upmarket Kolonaki neighbourhood and exploded at 7:10 am (0510 GMT), police said.
The police officer was hospitalised with minor injuries to his face and hands sustained when he went to inspect a “suspicious” package after being alerted by the caretaker.
The caretaker was also hospitalised.
A cafe worker nearby told Skai television the blast had been “powerful”.
Prime Minister Alexis Tsipras’ Syriza party condemned what it called an “atrocious act” and voiced support for the two wounded men.
Tsipras’ main domestic rival Kyriakos Mitsotakis, head of the New Democracy party, accused the government of tolerating repeated acts of violence and warned that “the feeling of insecurity” had reached a new level.
Socialist Party leader Fofi Gennimata said: “There is a problem of security in the country, the government must take responsibility.”
Anti-terrorist police have launched an investigation focused on anarchists or far-left groups.
Non-fatal attacks targeting centres of power, embassies, banks and media outlets have become common in Greece in recent years, and have often been blamed on such groups.
Ten days ago, a homemade bomb exploded outside the headquarters of the Skai media group in a seaside Athens suburb causing major damage. There have been no claims of responsibility.