Greek police on Monday were searching for four masked gunmen who burst into a popular restaurant a day earlier and shot dead two men from Montenegro.
One woman was wounded and hospitalized.
Police believe the case is potentially linked to the settling of accounts by Balkan criminal gangs.
The men were dining with their wives and two children, both aged 10, when the gunmen walked into the taverna in a coastal area south of Athens and shot them at around 6:30 p.m.
The wife of one of the two was wounded in the leg, possibly from a ricocheting bullet. Police said they recovered 24 shell casings from the scene.
The restaurant was not busy at the time.
The two men had pending international arrest warrants against them issued by Montenegro for participation in a criminal organization. It was unclear how long they and their families had been in Greece.