BUCHAREST (Reuters) -Romania scrambled fighter jets on Saturday when a drone breached the country's airspace during a Russian attack on Ukrainian infrastructure near the border, the defence ministry said.

A threat of drone strikes also prompted Poland to deploy Polish and allied aircraft and close an airport in the eastern city of Lublin, three days after it shot down Russian drones in its airspace with the backing of aircraft from its NATO allies.

Romania, a European Union and NATO state which shares a 650-km (400-mile) border with Ukraine, has had Russian drone fragments fall onto its territory repeatedly since Russia began waging war on its neighbour.

On Saturday, it scrambled two F-16 fighter jets and warned citizens in the southeastern county of Tulcea near the Danube and its Ukrainian border to take cover, the defence ministry said in a statement.

It added the jets detected a drone in national airspace, which they followed until it dropped off the radar 20 km southwest of the village of Chilia Veche.

"The drone did not fly over inhabited areas and did not pose an immediate danger to the population," the statement said.

NATO announced plans to beef up the defence of Europe's eastern flank on Friday, after Poland shot down drones that had violated its airspace, the first known shots fired by a member of the Western alliance during Russia's war in Ukraine.

Romanian lawmakers approved a law earlier this year enabling the army to shoot down drones illegally breaching Romanian airspace during peacetime, based on threat levels and risks to human life and property, but the bill does not yet have enforcement rules approved.

(Reporting by Luiza Ilie)