Moscow has repeatedly attacked Ukraine's ports in the south, including areas bordering Romania, since exiting a grain deal that aimed to protect grain exports through the Black Sea this summer.

According to the defence ministry, a 1.5-metre deep crater was found in an uninhabited area close to the town of Grindu in Tulcea county, which faces the Ukrainian port of Reni across the Danube.

The crater was the "result of (an) uncontrolled crash of a drone used in the attack on Ukrainian port infrastructure," the ministry said.

Russia's envoy would be summoned to explain this "new violation of Romania's airspace," the foreign ministry said.

It condemned Moscow's "repeated attacks" and said consultations with NATO allies "on developments at the Romanian-Ukrainian border" are underway.

NATO said it had no indication of an "intentional attack by Russia against allies."

But it strongly condemned "Russian attacks against civilian infrastructure in Ukraine (and) along the Danube."

F-16 and Eurofighter Typhoon fighter jets were also deployed to monitor the airspace.

In September and October, drone debris was discovered in Romania near its border with Ukraine, but officials stressed that the country had not been intentionally targeted.

As a result, measures to protect the population close to the border with Ukraine have been taken, including the construction of air-raid shelters in the eastern Romanian village of Plauru.

Ukraine said Thursday that its air-defence systems had destroyed more than 40 Iranian-designed drones launched by Russian forces targeting the southern city of Odesa.

burs-ani-kym/db