Authorities said they would use an unmanned drone from the United States to monitor and track any suspicious activity.
The fire posed no immediate threat to Greece's famed ancient monuments, but as it raged inland, children's' summer camps and holiday homes were hastily abandoned.
Eleven people were seriously injured, he added, while 16 of those injured were children.
At least five of those who died were killed as they tried to escape from the flames into the sea.
Newspaper printed banner headlines including "Killer Fire" and "Hell" and reported fears the death toll would climb.
By early evening, a huge plume of smoke was visible on Acropolis hill.
A firefighter tries to extinguish hotspots during a wildfire in Kineta, near Athens, on July 23, 2018.
"It burned our backs and we dived into the water".
A firefighting helicopter flies over an avenue during a forest fire in Neo Voutsa, a northeast suburb of Athens, Greece, July 23, 2018.
Prime Minister Benjamin Netanyahu phoned his Greek counterpart Tuesday to offer condolences after wildfires killed dozens of people near Athens.
Giorgos Mathiopoulos, the head of Greece's emergency workers association, told reporters that one fire broke out around noon and the second around 5 p.m.
People jammed roads and freeways, trying to get away from the fires only to be trapped in their cars by the deadly flames.
AFP photoA man walks among burnt cars following a wildfire at the village of Mati, near Athens, on Tuesday. A search-and-rescue team, made up of 130 Armed Forces personnel and firefighters, combed the hard-hit areas of Voutsa, Mati and Rafina looking for victims, officials said.
People watch a wildfire in the town of Rafina near Athens on July
Fire swept through the village 40km (25 miles) north-east of Athens on Monday and was still burning in some areas on Tuesday morning.
"The Australian embassy in Athens has confirmed with local authorities that no Australians are known to be affected by forest fires near Athens at this time", a spokesperson for DFAT said.
"What concerns us is that there are fires occurring simultaneously". "Then the patrol boats came".
Evacuees were transferred to hotels and military camps, while anxious relatives flocked to the area. It was also searching for a boat reported missing that was said to be carrying Danish tourists fleeing the fires.
Yannis Stratikopoulos of the civil protection agency said it is too early to speculate on what caused the fires.
Emergency services were banking on a drop in the wind but the forecast for the region - which has experienced temperatures topping 40 Celsius (104 Fahrenheit) - suggest conditions would remain challenging into Tuesday.
In the north of the country, more than 300 firefighters, five aircraft and two helicopters were mobilised to tackle the "extremely difficult" situation, Athens fire chief Achille Tzouvaras said.
It is believed the blaze started in a ravine located in the mountains overlooking Kineta, a resort town some 54 kilometres west of Athens.
Greece sought help in fighting the fires from the European Union. "I think she was burned herself here", he said.
"We will do whatever is humanly possible to control it", Prime Minister Alexis Tsipras told reporters.
Officials have asked for U.S. drones "to observe and detect any suspicious activity" as it emerged 15 fires had started at the same time in three different areas near Athens - possibly by criminals intending to ransack homes once they were abandoned by fleeing residents.
The group, which included children, were found near the top of a cliff overlooking a beach.
A spokesperson for the Irish Department of Foreign Affairs said it is "providing consular assistance to a number of individuals in Greece".