Ukraine's air defense units destroyed 15 of 23 attack drones and one guided air missile launched by Russia overnight, Ukraine's air force said on Sunday.

NATO member Romania shares a 650-km (400-mile) border with Ukraine and has had Russian drone fragments stray into its territory repeatedly over the past year.

Along the Danube River, Romanian territory is just a few hundred metres from Ukrainian river ports which have been repeatedly hit.

During the strike, "the radar supervision system identified and tracked the path of a drone which entered national airspace and then exited towards Ukraine", the defense ministry said in a statement condemning the attack.

Romania scrambled two F-16 fighter jets to monitor the attack. Residents of the southeastern Romanian counties of Tulcea and Constanta were warned to take cover.

"From existing data, the possibility of an impact zone on national territory was identified, in an uninhabited area near the village of Periprava," the ministry added.

Ministry personnel were searching the area.

Romanian lawmakers have yet to approve legislation enabling the country to shoot down drones invading the country's airspace during peacetime, with plans to do so in the current legislative session.

"There weren't serious issues on the ground," Romanian Prime Minister Marcel Ciolacu told reporters on Sunday after consulting with the defense minister.

"(Attacks) will continue. That is it, we have a war on the border."