Drones could soon handle mid-air refuelling by themselves, without the involvement of human pilots, US military flight tests have shown.
The findings raise the possibility of automated "flying gas stations" topping off robotic aircraft over future battlefields.
The CIA regularly uses unmanned drones to target militants in countries like Pakistan, Afghanistan and Yemen. The US Defence Advanced Research Projects Agency (DARPA) recently flew two modified RQ-4 Global Hawk drones in close proximity to simulate mid-air refuelling.
Meanwhile, a European commission report predicts hundreds of civil uses for unmanned aircraft in the next decade. But the claims have prompted concerns that the unmanned aircraft will result in more forms of surveillance.
Some 95% of drones in operation are used by military, but the document says they now also have 'great potential for civil applications'.