Drone fragments in the wake of Russian attacks have been found in Nato member Romania’s territory three times following such attacks this month, underlining security risks for the North Atlantic alliance, whose members have a mutual defence commitment.

Russian attacks on Ukraine’s river ports across the Danube from Romania have increased since mid-July when Moscow abandoned a year-old deal that lifted a de facto Russian blockade of Ukraine’s Black Sea ports.

Nato has said Russian strikes near the border were “destabilising” even if there was no indication that Russia intended to hit a Nato member.

Romania first enforced restrictions along the border with Ukraine in May last year, up to 8km inside its national airspace, to a height of up to 1,000m.

On Thursday, the ministry said it has enforced additional restrictions between its Danube river ports of Sulina and Galati for up to 30km inside its national airspace up to a height of 4,000m.

“Manned or unmanned aircraft are not allowed in these restricted areas, except for state aircraft…and emergency situations,” the ministry said in a statement.

“Given the intensifying Russian attacks on Ukraine’s river ports, measures to extend restrictions were necessary to ensure a more efficient monitoring and control of air space.”

Romania’s foreign ministry has summoned the Russian charge d’affaires twice after the discovery on Romanian soil of drone fragments.

The defence ministry is set to deploy additional troops to southeastern Romania near the border and increase patrols and observation points, seeking to prevent risks to local residents.

Ukraine is one of the world’s biggest grain exporters and the Romanian Black Sea port of Constanta is now Kyiv’s largest alternative export route, with grains arriving by road, rail, or barge across the Danube.