Cabinet spokesman Stelios Petsas said the conservative government made the decision this year after tens of thousands of asylum seekers tried to enter the European Union member state in late February when Turkey said it would not try to stop them.
Greece is Europe’s gateway to people fleeing conflicts in the Middle East and other regions, and more than a million migrants passed through their borders in 2015 and 2016.
Petsas added in a press briefing that the project, which is being implemented by four Greek companies, will be completed within eight months at costs amounting to 63 million euros.
Petsas, without going into details, indicated that the fence would extend in areas recommended by the army and police.
Athens announced in March that the fence, currently 12.5 km long, would be increased to 40 km.
Tensions have escalated recently between Greece and Turkey due to exploration for oil and gas resources in the eastern Mediterranean region, and the two countries in NATO differ on the beginning and end of the continental shelf for each of them.