The German-led "Air Defender 23" will run until June 23 and include some 250 military aircraft from 25 NATO and partner countries including Japan and Sweden, which is bidding to join the alliance. Finland, which is just became a NATO country, will also participate in the exercise.
Up to 10,000 people will participate in the drills intended to boost interoperability and preparedness to protect against drones and cruise missiles in the case of an attack on cities, airports or sea ports within NATO territory.
Presenting the plans last week, Lieutenant General Ingo Gerhartz of the German Luftwaffe said "Air Defender" was conceived in 2018 in part as a response to the Russian annexation of Crimea from Ukraine four years before, though he said it was "not targeted at anyone".
He said that while NATO would defend "every centimeter" of its territory, the exercise would not "send any flights, for example, in the direction of Kaliningrad," the Russian enclave bordering alliance member states Poland and Lithuania.
"We are a defensive alliance and that is how this exercise is planned," he said.
US Ambassador to Germany Amy Gutmann said she intended to send a message to countries including Russia.
"I would be pretty surprised if any world leader was taking note of what this shows in terms of the spirit of this alliance, which means the strength of this alliance, and that includes Mr. Putin," she told reporters, referring to the Russian president.
"By synchronizing together, we multiply our force."
NATO's air exercise came just after Ukraine launched a counter-offensive. As part of the Ukrainian counter-offensive, a major battle erupted in southeastern Ukraine.
Kyiv says it has liberated four villages in the south-east, calling these the first settlements won back from Russia since Kyiv's counter-offensive began.
Footage shared on Monday morning showed the Ukrainian flag flying in the Donetsk region.
Ukrainian President Volodymyr Zelenskyy made his first public comments on Ukraine's counteroffensive, which began last week.
"Counteroffensive and defensive actions, accordingly, are taking place in Ukraine, on which stage, I won't say in detail," Zelenskyy said.
"I think we should trust our militaries. And I trust them. I am in touch with our commanders of different areas every day. Everyone is optimistic. Pass this to [Russian President Vladimir] Putin," he added.
Source: Greek Reporter