ATHENS, Greece (AP) — Greece formally approved an offer to buy 20 F-35 Joint Strike Fighters from the United States as part of a major defense overhaul, government officials said Thursday.

“The letter of acceptance for the F-35s has been signed and sent to the United States,” Defense Minister Nikos Dendias said while visiting a military air base near Athens.

The purchase, he said, would create “a powerful deterrent presence in our region.”

Delivery of the fifth-generation jet made by Lockheed Martin is expected to start in 2028, while Greece maintains the option to purchase 20 additional F-35 jets as part of an $8.6 billion deal.

The purchase of the first 20 jets along with additional support will cost some $3.5 billion, Greek officials said.

Greece is overhauling its military in a decade-long program following a protracted financial crisis and continued tension with neighbor and NATO ally Turkey, mostly over a volatile sea boundary dispute.

Turkey was dropped from the F-35 program five years ago over its decision to buy Russian-made S-400 surface-to-air missile system, a move seen in the United States as a compromise to NATO security.

In Athens, government spokesman Pavlos Marinakis described the current military modernization campaign as the most significant in “many decades.”

“We will continue to implement this major program, equipping our country and armoring its defenses,” Marinakis said.

Athens has been seeking an advantage in the air since Turkey’s exclusion from F-35 purchases and has also acquired advanced French-made Rafale fighter jets. Deliveries to the Greek air force began in 2021, starting with jets previously used by France’s military that will be supplemented by new aircraft built by French defense contractor Dassault Aviation.

The U.S. State Department in January approved the sale that could eventually total 40 F-35 aircraft, along with 42 engines as well as services and equipment including secure communications devices, electronic warfare systems, training, logistics, and maintenance support.