NATO allies in Germany prepared for an unprecedented air deployment exercise over Europe today in what US diplomats said was a warning to Russia’s Vladimir Putin.

German and US officials said that the Air Defender 23 exercise starting next week will involve 10,000 participants and 250 aircraft from 25 nations responding to a simulated attack on a Nato member country.

The United States alone is sending 2,000 Air National Guard personnel and about 100 aircraft to take part in the June 12-23 training manoeuvres.