Two drones were spotted flying over a German military base earlier this week, just two days after a drone carrying explosives was found at a cargo airport, the German Armed Forces said on Saturday.

Security surveillance at the Bundeswehr base in Mechernich reported seeing two drones around 10 p.m. on Thursday, according to a statement from the German Joint Force Command. The sightings were confirmed and military police forces deployed to the site.

The military said the Euskirchen police department has opened an investigation. The police did not immediately respond to a request for comment and the military did not release additional details.

Recently, drone sightings over civilian and cargo airports have been reported more frequently. Last year, mysterious drone flights over the airspace of European Union member countries alarmed the public and authorities and also prompted the cancellation of dozens of flights that stranded thousands of passengers.

The drone with explosives was found at Germany’s Leipzig/Halle Airport – a major hub for international freight – shortly before midnight on Tuesday. While the device was defused, its discovery earlier is assessed by the U.S. to be of Russian origin, officials told CBS News.

The airport is home to NATO’s Strategic Airlift International Solution, or SALIS, which is currently operational almost every day in delivering equipment to NATO battle groups along its eastern flank from Finland to Romania and supporting EU and alliance nation missions.

The recent incidents come as American intelligence assessments indicate Russian President Vladimir Putin could be increasingly willing to authorize provocative actions that could extend onto NATO territory, U.S. officials briefed on the matter told CBS News.

Western officials have accused Russia and its proxies of staging dozens of attacks and other incidents – including Russian drone incursions into Romania and a broader uptick in suspected sabotage and cyber operations across Europe since the full-scale invasion of Ukraine more than four years ago.

The Russian Embassy in Germany on Friday called the Leipzig drone incident part of a “new wave of anti-Russian hysteria in Germany.”