Unidentified drones were spotted over a Belgium military base housing U.S. nuclear weapons, sparking security concerns and an investigation into a potential spying operation.

Belgium will work to improve surveillance of its airspace following repeated sightings of drones over its airports and military bases, Defence Minister Theo Francken said on Thursday. Belgium's Brussels and Liege airports were closed for hours on Tuesday evening after drone sightings,

Belgium's defense minister said that more counter-uncrewed aerial systems "are urgently needed" after three drones spied on the Kleine-Brogel base.

A number of high-profile drone espionage incidents have alarmed European NATO members—but it is not yet clear which adversary, if any, is responsible.

Mobile phones detected at sensitive sites, including nuclear plants, NATO headquarters, military bases, finds investigation by European media outlets - Anadolu Ajansı

Several drones spotted above a Belgian airbase over the weekend were there “to spy” on military fighter jets, the country’s defense minister said Sunday, at a time when European nations are on high alert for airspace intrusions.

Belgium’s defense minister says a number of drone flights over the weekend near a military base where U.S. nuclear weapons are stored could be part of a spying operation.

Belgium's defence minister Theo Francken hit back at Russia's nuclear threats with Selena Gomez's 'Calm Down'.

Belgian telecom operators Proximus and Scarlet experienced brief disruptions early Wednesday following a DDoS, or Distributed Denial of Service cyberattack, according to the Belga news agency.​​​​​​​

Analysts say Kleine Brogel is one of a handful of European military bases hosting U.S. tactical weapons, an estimated 10 to 15 B-61 nuclear bombs that can be dropped from nuclear-capable F-16 jets. The base describes itself as a key part of NATO's nuclear deterrence strategy. In the alliance, only the U.S., the U.K. and France have nuclear weapons.