Russian fighter jets flew without permission into the airspace above Estonia, a NATO member nation, for 12 minutes, Estonia’s foreign minister said on Friday, in what he described as “clear proof of Russia’s growing aggression.”

Russia regularly infiltrates the airspaces of NATO countries to test their readiness and resolve. Russian jets had previously entered Estonian airspace four times this year, the minister, Margus Tsakhna, said, according to local news media.

But he described Friday’s incursion, by three MIG-31 fighters over the Gulf of Finland, as an “unprecedented and brazen intrusion.”

“Such actions,” he added, “cannot be tolerated and must be met with swift political and economic pressure.”

The incursion came a little over a week after more than a dozen Russian drones entered Poland, prompting NATO to scramble fighter jets to shoot them down in what Western officials described as a dangerous escalation of the war in neighboring Ukraine.

This is a developing story. Check back for updates.