NATO member Romania announced Tuesday that it has begun building air-raid shelters for residents near the Ukraine border, after drone fragments were found there last week.

Romanian soldiers on Saturday found fragments of a drone "similar to those used by the Russian army" in the Plauru area across the border from Ukraine.

Bucharest has already beefed up measures to strengthen monitoring and airspace security following repeated Russian attacks close to its border.

Approximately 50 Romanian soldiers began building two shelters on Tuesday, the defence ministry said in a statement. 

The concrete shelters are aimed at "protecting the residents" of Plauru and will be handed over to local authorities once completed, it added.

The move follows a decision by the Romanian National Committee for Emergency Situations to adopt "protection measures on the national territory in the immediate vicinity of the conflict zone in Ukraine".

Romanians living in the area close to the Ukrainian ports of Reni and Izmail will also be alerted on their phones in case of any "risk from the fall of elements" related to the war.  

Moscow has ramped up attacks on Ukraine's southern Odesa and Mykolaiv regions, home to ports and infrastructure vital for agriculture exports following the collapse of a deal allowing grain shipments from Black Sea ports.

Romanian President Klaus Iohannis and NATO chief Jens Stoltenberg discussed the drone fragment discovery on Saturday.

Stoltenberg said on X, formerly Twitter, there was "no indication of intent to hit NATO, but the strikes are destabilising".

Iohannis said the discovery indicated "there took place an absolutely unacceptable breach of the Romanian sovereign airspace".

Since Russia's all-out invasion of Ukraine in February last year, NATO has been focused on preventing the war from spilling over onto its territory.