Athens will deploy the missiles at Saudi cost "to protect critical energy infrastructure," government spokesman Stelios Petsas told reporters.

"The deployment contributes to energy security, promotes our country as a factor of regional stability and strengthens our ties to Saudi Arabia," Petsas said, adding that talks on the move began in October.

He did not give a date for the deployment.

The US, Britain and France are part of the same initiative and Italy is likely to join, the spokesman said.

The announcement came as Greek Prime Minister Kyriakos Mitsotakis was on a Middle East tour for investment talks with the governments of Saudi Arabia and the United Arab Emirates. He visited Riyadh on Monday and is in Abu Dhabi on Tuesday.

"As a defensive system, this constitutes no threat to other countries in the area," Petsas said.

Earlier this week Petsas said that "around 130 personnel" would accompany the missiles.

Greek opposition parties have condemned the move as dangerous "adventurism."

"This would be a Greek military presence outside the Mediterranean for the first time in decades," leftist Eurodeputy Dimitris Papadimoulis tweeted in January.