Turkey has officially requested the extradition of eight military officers who fled the country after July's failed coup, Greek officials said Thursday.

"The demand was received yesterday and sent to the justice ministry," a diplomatic source told AFP.

The eight men -- two commanders, four captains and two sergeants -- requested asylum in Greece after landing a military helicopter in the northern city of Alexandroupoli four days after the attempted government takeover on July 15.

Their asylum hearings are to begin on Friday, when two of the officers are scheduled to appear before a committee.

In late July, the court of Alexandroupoli sentenced the eight -- who face a military trial in their homeland if sent back -- to suspended two-month prison terms for illegal entry.

The men were subsequently relocated to Athens and are in police custody until their asylum applications are heard, a process expected to take a month.

The eight claim they will not receive a fair trial in Turkey, where the authorities have detained thousands of people over the coup, including top generals.

If sent home, their lives could be in danger, one of their lawyers has claimed.

Rights group Amnesty International has said it has "credible evidence" of the abuse and torture of people detained in sweeping post-coup arrests -- something Ankara has denied.

The case threatens to strain ties between the uneasy NATO allies, with Ankara labelling the eight "terrorists".