According to two senior defense officials, Romania is relocating air defenses closer to its Danube villages across the river from Ukraine, where Russian drones have been striking grain facilities, and is increasing military observation stations and patrols in the region.

The steps, together with the deployment of four extra US F-16 fighter planes and an enlarged no-fly zone, reflect rising anxiety in Romania and the NATO alliance that the Ukraine conflict would spill over onto its territory.

A missile hit southern Poland in November, killing two people and causing a momentary security worry, but it was eventually discovered that Ukrainian air defenses were to fault. Romania is currently in the limelight.

Soon after pulling out of the Black Sea grain deal on July 17, Moscow began targeting Ukrainian ports and warehouses along the Danube, in an apparent attempt to choke off the main alternative route for Ukraine’s agricultural exports.

Among the targets were the Ukrainian ports of Izmail and Reni, both of which lie across the Danube from Romanian soil.

Isolated incidents of drone parts landing in Romania underline the risk of a misunderstanding, or worse, between Russia and NATO, prompting Romanian armed forces to increase security in the area to protect civilians, the two sources said.

They declined to be named in order to discuss sensitive security matters.

The army has built two bomb shelters in the small hamlet of Plauru, just a few hundred metres from Izmail, and residents in the wider area are sent alerts on mobile phones when Russian drones are detected heading in their direction.

Tudor Cernega, mayor of the commune of Ceatalchioi which includes the hamlet of Plauru, said, however, that poor mobile reception there limited the effectiveness of the warnings.

In a statement last Friday Romania’s defence ministry said that around 100 U.S. troops and four U.S.-designed F-16 Fighting Falcon jets had arrived at Borcea military air base around 150 km south of Izmail.

From mid-September, the ministry also expanded a no-fly zone along a section of the border with Ukraine to up to 30 km (20 miles) inside Romania and to a height of 4,000 metres as a deterrent against Russian drones entering Romanian air space to reach enemy targets.