A military helicopter carrying eight soldiers who were allegedly involved in Turkey's attempted coup has landed in Greece.

All those on board the Black Hawk helicopter, which gave a distress signal shortly before landing in the northeastern city of Alexandroupolis, have been arrested for entering the country illegally.

Turkey's Foreign Minister Mevlut Cavusoglu says Athens has asked Ankara to "extradite the eight traitors as soon as possible".

The soldiers - who reportedly include two majors, four captains and two sergeants first class - have requested political asylum, and Greece has said it will examine their request on Sunday.

A Greek government spokeswoman said: "We will follow the procedures of international law. However, we give very serious considerations to the fact that (the Turkish military men) are accused, in their own country, of violating the constitutional order and trying to overthrow democracy."

Earlier on Saturday, Greek Prime Minister Alexis Tsipras had expressed his support for the "democratically elected" Turkish government.

Arrangements are now being made to return the helicopter to Turkey "as soon as possible".

More than 2,800 military personnel in Turkey have been arrested after a group calling itself the Council for Peace in the Homeland declared martial law and a curfew.

The country does not have the death penalty, but prime minister Binali Yildrim says changes to the law may be considered in order to deter dissidents from staging another coup in the future.