A criminal investigation is underway following reports from the U.S. Air Force of drone sightings over several English military bases, as confirmed by a British official on Wednesday.

The incursions were noted over the past week at four installations where American forces are stationed. The U.S. Air Force is actively monitoring this situation and has implemented various unspecified countermeasures to address the threats posed by the drones.

The Ministry of Defense Police, alongside local agencies and U.S. military personnel, is conducting a thorough investigation into these drone activities, as stated by Defense Minister Vernon Coaker during a parliamentary session.

Coaker emphasized, “We take any safety issue seriously and maintain robust measures at Ministry of Defense sites. This includes counter-drone capabilities.” He also warned that individuals found guilty of related offenses could face prison sentences of up to 14 years under existing national security laws.

While the motives behind the drone flights remain unclear, the incidents occur amidst escalating tensions related to the ongoing conflict in Ukraine, which has witnessed intensified hostilities since Russia’s large-scale invasion nearly three years prior.

The situation has been further complicated following Ukraine’s recent strikes on Russian targets using intermediate range missiles supplied by the United States and the United Kingdom after President Biden approved their usage. In response, President Putin declared that Russia retains the right to target countries that facilitate such military actions against it.

The unauthorized drone activity, which began on November 20 and included multiple incursions on Tuesday, was detected above or near RAF Lakenheath, RAF Mildenhall, and RAF Feltwell located in eastern England, as well as RAF Fairford in the southwest.

RAF Lakenheath is known for hosting the 48th Fighter Wing, a vital component of the U.S. Air Force’s combat capabilities in Europe. Concurrently, RAF Mildenhall is home to the 100th Air Refueling Wing, while RAF Feltwell serves as a central hub for various housing and service needs, including schools. Lastly, RAF Fairford accommodates the 501st Combat Support Wing Headquarters and the 420th Air Base Squadron.

Additionally, Coaker reported that a drone was also observed last Friday flying approximately 250 meters (273 yards) from the HMS Queen Elizabeth, the Royal Navy’s flagship aircraft carrier, as it made its way into the German port of Hamburg.