Trident Juncture, NATO's largest military operation in 13 years, opened on Monday in the Mediterranean, in what General Philip Breedlove described as "a very clear message to any potential aggressor."

The land, air and sea exercise involves some 36,000 soldiers, sailors and air force troops from 30 countries, and is built around a fictious operation involving a rogue state threatening trade and energy supplies in Africa. The operation is hosted by Italy, Spain and Portugal, and also includes non-NATO members like the Ukraine and the African Union.

Earlier on Monday, NATO Deputy Secretary General Alexander Vershbow took to Twitter to defend the maneuvers.

The operation, which began with a lavish opening ceremony, comes as Russia has stepped up its military campaign in the Middle East. Earlier this month, Moscow drew criticism for twice violating the airspace of Turkey, a NATO member, while the western alliance has repeatedly criticized what it considers creeping Russian involvement in Eastern Europe.

After the Turkish airspace violations earlier this month, NATO's Jens Stoltenberg issued a not-so-subtle warning to Russia's Vladimir Putin.

"NATO is able and ready to defend all allies, including Turkey, against any threat," Stoltenberg said.

That statement was echoed by Vershbow on Twitter Monday.

In addition to soldiers, more than 140 aircraft and 60 ships will particpate in the operation, which is expected to run through November.

blc/msh (Reuters, dpa, AP)