TALLINN, Estonia (AP) — Estonia on Wednesday summoned Russia’s ambassador over an airspace violation by a Russian military aircraft.

Foreign Ministry spokeswoman Mari-Liis Valter said Estonia considers the violation serious. She said the Baltic country “demands an explanation” as to why a Russian Ilyushin-20 surveillance aircraft crossed into its airspace Tuesday afternoon.

Estonia’s military said earlier the plane had entered Estonia’s airspace for around one minute.

NATO said in a statement fighter jets from Denmark, Portugal, as well as non-NATO member Sweden were involved in intercepting the Russian aircraft as it flew over the Baltic Sea.

It said the aircraft entered Estonian airspace near the island of Saaremaa — an incursion of about 600 meters (656 yards) into NATO airspace.

The incident comes as Russian forces have been accused of a series of border violations.

Since Friday, the Swedish Navy has been combing the Stockholm archipelago for signs of a foreign submarine that officials suspect entered its territorial waters illegally. It hasn’t officially linked Russia to the suspected intrusion, but many analysts say Russia would be a likely culprit.

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