Shots were also fired at a person guarding the Athens Appeal Court building, Justice Minister Stavros Kontonis told state TV. The Justice Ministry suspended the court's operation for one day.
Over 6,700 illegal Pakistani immigrants entered EU, SC told
There were no reports of injuries. Two Greek media organisations received warning calls at 2:50 am (0050 GMT), before the explosion, one official said.
Police, who had cordoned off the area, later found a bag which contained the makeshift bomb outside the building. Police were also investigating footage from cameras nearby, another official said, and reports of two people leaving the scene in a van.
115 Pakistanis detained in Turkey over illegal migration
Small-scale attacks on businesses, state buildings, police and politicians are frequent in Greece, which has a long history of political violence. Public anger remains high after seven years of belt-tightening in a crisis that has cut thousands of jobs and eroded living standards.
Protesters have repeatedly tried to block foreclosure auctions of home at courts, a key condition of Greece's international bailout. Electronic auctions started in November.
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