Belgium’s National Security Council convened an emergency meeting Thursday to address an unprecedented surge in drone sightings over the past week near airports and military bases across the country. On Tuesday, unidentified drones were spotted near every major airport in Belgium, prompting a temporary closure of national airspace.

While officials have not made any public statements regarding responsibility, sources within Belgian security services said there is “little doubt” that a state actor is behind the incidents — “very probably Russia.”