Ending months of negotiations, the US government on Friday okayed the $8.6-billion sale, as well as a separate $23-billion deal to sell 40 F-16 warplanes to Turkey.

"Today is an important day for our national defence and for Greek diplomacy," Mitsotakis said in a statement.

"Greece is officially on track to acquire up to 40 new generation F-35 combat planes."

Mitsotakis said he had received a letter from US Secretary of State Antony Blinken which "showed the strategic strength of Greek-US relations".

In the letter, Blinken said: "Greece has taken remarkable steps to modernize its defense capabilities. I look forward to increasing our cooperation and developing a more robust strategic relationship between our armed forces."

As required by US law, the State Department notified Congress of the agreements, which were held up until Ankara ratified Sweden's NATO membership.

In addition to the F-35s, Greece will "acquire for free a very large quantity of equipment which will decisively strengthen the three branches of the armed forces and the Greek coastguard service," the prime minister said.

This includes frigates, C-130 cargo planes, tanks, armoured vehicles and numerous other pieces of military equipment.

Greece has been seeking for some time to buy more sophisticated F-35 jets from the US as part of its strategy of defence against Turkey, with which ties are often strained.

Athens vigorously opposed the sale of US F-16s to Ankara, due to a dispute over maritime borders in the eastern Mediterranean, which is rich in energy resources.