"The report reflects the threats as perceived by the country's military," a defence ministry official told Reuters. "It considers the continuing instability in the Balkans as a serious threat, more serious than Turkey at this very moment."
Greece shares northern and northwestern borders with Albania, the former Yugoslav Republic of Macedonia (FYROM) and Bulgaria.
Turkey comes second as a defence and security threat to Greece for the first time since the division of the island of Cyprus following the 1974 invasion by Turkish troops after a failed coup backed by Athens.
The report, a briefing sheet of which was made available on Wednesday, cites improved bilateral ties with Turkey and notes Greece's support of its neighbour's bid to join the European Union.
STAUNCH ALLY OF EU BID
Athens is a staunch ally of Ankara's drive to join the EU, saying membership would greatly improve bilateral relations as well as add to stability in the eastern Mediterranean.
"But it (Turkey) has not shifted its policies regarding sovereign territory of our country and a sufficient deterring force must be maintained," the report said.
Greece shares eastern land borders with Turkey and dozens of its Aegean islands are close to the western Turkish coast.
Apart from the ethnically divided island of Cyprus in the eastern Mediterranean, Greece has other territorial disputes with Turkey in the Aegean. The two NATO members in 1996 almost went to war over an uninhabited islet in the southern Aegean.
Ties with Ankara have considerably improved in the past six years and the two neighbours have pledged to reduce their high defence budgets in a bid to boost confidence and unlock much-needed funds for social projects.