Turkish jets carrying out missions over the Aegean and Eastern Mediterranean were harassed by a Greek S-300 air defense system, according to Turkish Defense Ministry sources.

Turkish jets were "radar locked" on Aug. 23 on a mission in international airspace, said the sources, requesting anonymity due to restrictions on speaking to the media, describing the Greek harassment as a "hostile act" according to the NATO rules of engagement.

"Despite this hostile act, the planes completed their planned missions and returned to their bases safely," the sources added.

The harassment came from a Russian-made S-300 air defense system stationed on the island of Crete, the sources stressed, mentioning how some NATO countries continue to criticize Türkiye for buying Russian-made S-400 systems but say nothing about Greece.

Telling how Greece bought the previous version of the system nearly 25 years ago, sources say that a NATO country, namely Greece, harassing another NATO country's warplanes through the Russian-made S-300 system is "against the principles of the NATO alliance."

Türkiye, a NATO member for over 70 years, has complained of repeated provocative actions and rhetoric by Greece in the region in recent months, saying such moves frustrate its good faith efforts for peace.

In April 2017, when its protracted efforts to buy an air defense system from the United States proved futile, Türkiye signed a contract with Russia to acquire the state-of-art S-400s.

U.S. officials voiced opposition to their deployment, claiming the S-400s would be incompatible with NATO systems.

Türkiye, however, stressed that the S-400s would not be integrated into NATO systems, and pose no threat to the alliance or its armaments and has repeatedly proposed setting up a commission to clarify the issue.

Greece is wasting its people's money on second-hand weapons to use against Türkiye, Defense Minister Hulusi Akar said Friday, reiterating criticism of Athens' aggressive armament and provocative actions against Türkiye.

Speaking to Turkish broadcaster A Haber in an exclusive interview, Akar underlined that Greece has launched a futile armament campaign.

"Greek people's money is wasted on weapons and equipment that have completed their economic life. Used planes, used tanks, used cannons, whatever they had, France sells them to Greece and makes money. You won't get anywhere with that, though. If you are trying to defend Greece with your work, this is too much for defense. You don't need that many weapons to defend. But if this is against Türkiye, this is not enough."

Neighbors and NATO allies Türkiye and Greece are at odds over a number of issues, including competing claims over jurisdiction in the Eastern Mediterranean, overlapping claims over their continental shelves, maritime boundaries, air space, energy, the ethnically split island of Cyprus, the status of the islands in the Aegean Sea and migrants.

In recent months Türkiye has stepped up criticism of Greece stationing troops on islands in the Eastern Aegean, near the Turkish coast and, in many cases, visible from the shore. These islands were required to be demilitarized under the 1923 Treaty of Lausanne and the 1947 Treaty of Paris, so any troops or weapons on the islands are strictly forbidden. Also, Türkiye and Greece have traded accusations of airspace violations in recent months.

Despite saying that it has no intention of entering into an arms race with its neighbor and NATO ally Türkiye, Greece also continues to carry out an ambitious rearmament program for its armed forces. Greece's burgeoning arms program is designed to counter the protection of Turkish interests in the Eastern Mediterranean. Türkiye has often warned Greece against indulging in an arms race, offering to resolve all outstanding issues, including in the Aegean, the Eastern Mediterranean and the island of Cyprus, through dialogue.