Groups of youths on Monday afternoon attacked and vandalized two bank branches in Athens, using stones, sticks and other objects, and no injury was reported.
The incidents occurred at around 2 p.m. local time. Youngsters broke the windows of the National Bank of Greece branch in the centre of Athens and a Proton Bank branch in the city.
Earlier Monday, a strong explosion occurred at 3 a.m. local time outside a Citibank branch in Athens' north eastern suburb.
The home-made explosive device had been planted at the rear of the bank, and caused extensive damage to the bank and to cars parked near by.
The police counter-terrorism squad was investigating the incident.
Since a 15-year-old boy killed by police last December, Athens witnessed a series of protests and bomb attacks which aroused the worst riots in the country for decades.