(VOVworld) - A bomb exploded outside the offices of Greek business federation Hellenic in central Athens early on Tuesday, police officials said, smashing windows but causing no injuries. The blast, which police believe was carried out by domestic guerrilla groups, is the first such incident since leftist Prime Minister Alexis Tsipras came to power in January. The device, triggered by a timer and placed in a backpack near the entrance of the Hellenic Business Federation offices, went off around 3:30 am local time. An anonymous caller warned a newspaper some 30 minutes earlier, a police official said on condition of anonymity.