NATO has launched an initiative to reinforce the defense of Europe’s eastern flank after a Russian drone incursion into Polish airspace this week, NATO Secretary General Mark Rutte announced on Friday.

The “Eastern Sentry” operation will commence in the coming days and will involve assets from Denmark, France, the United Kingdom, Germany, and others, Rutte said.

“Eastern Sentry will add flexibility and strength to our posture and make clear that, as a defensive alliance, we are always ready to defend,” he added.

Rutte said that Russia’s “dangerous and unacceptable” drone incursion on Wednesday was “not an isolated incident.”

Among the equipment dedicated to the operation are two F-16s and an anti-air warfare frigate from Denmark, three Rafales from France, and four Eurofighters from Germany, according to a press release from the alliance.