Ukraine launched a major long-range strike on a key military airbase deep inside Russia that houses nuclear-capable bombers.

In the early hours of Thursday, a swarm of drones hit the Engels base, more than 400 miles from Ukraine’s front line, in the third such attack in 10 weeks, resulting in a series of explosions.

It came a day after Ukraine said it was willing to commit to the US-proposed temporary ceasefire on strikes on civilian and energy infrastructure, to which Moscow had already claimed to have agreed.

As a clear military target, Engels – considered one of Russia’s most important military facilities – near the city of Saratov in southern Russia, would not constitute a breach of such a truce.