A drone carrying explosives entered Bulgaria from neighboring Romania and detonated near a major international gas pipeline on Saturday, prompting heightened surveillance along the border between the two NATO members.

The drone exploded shortly after 5 a.m. about 330 feet inside Bulgarian territory, said Prime Minister Rumen Radev. The blast occurred in a sunflower field near the village of Kardam, around 200 meters from a Romanian compressor station and 1 kilometer from Bulgaria’s compressor station on the Trans-Balkan gas pipeline.

No casualties or damage to infrastructure were reported, and authorities cordoned off the area while investigating the incident, Radev said. The pipeline runs through the Balkans and connects Turkey with Ukraine.

The drone’s origin and any connection to Russia or Ukraine were initially unclear. Bulgaria’s Defense Ministry later said a preliminary analysis of the wreckage indicated that it was most likely a Maya decoy drone, a type widely used by the Ukrainian armed forces, according to The Associated Press.

“At this time, there is no reason to believe that the incident was intentional,” the ministry said in a statement.

Neither Romania nor Bulgaria detected or identified the drone before the explosion. Romania’s Defense Ministry said its radar surveillance systems had registered no aerial target whose trajectory indicated that it had crossed Romanian airspace toward Bulgaria.

Radev said Bulgaria would strengthen surveillance and move anti-drone detection and countermeasure equipment from its border with Turkey to the Romanian frontier. Bulgarian Defense Minister Dimitar Stoyanov said Sofia planned to raise the incident at a meeting of NATO’s North Atlantic Council early next week.

Given the size of the blast and the volume of black smoke, the unmanned aircraft appeared to have carried significant levels of explosives, Stoyanov said, adding that such drones are hard to detect because of their relatively small size and low flight paths.

Why the Trans-Balkan Pipeline Matters

The Trans-Balkan pipeline connects the gas networks of Turkey and Ukraine through Bulgaria, Romania and Moldova. The system can carry gas in both directions, making it a potential supply route for Ukraine and other countries in Eastern Europe.

The blast occurred near the Negru Vodă-Kardam interconnection point, which links the Bulgarian and Romanian transmission systems. Officials reported no damage to the pipeline or other infrastructure.

The route has taken on greater strategic importance amid efforts to diversify regional energy supplies and provide Ukraine with access to gas from southern Europe, including liquefied natural gas delivered through Greece, according to Romanian gas transmission operator Transgaz. The gas network operators of Greece, Bulgaria, Romania, Moldova and Ukraine have offered capacity along the route for deliveries northward to Ukraine.

Russia Launches Overnight Strikes on Ukraine

Russia launched six ballistic missiles and more than 150 drones at Ukraine overnight, killing four people in Kyiv and the surrounding region, Ukrainian authorities said. Air defenses intercepted 135 drones, but the ballistic missiles penetrated Ukraine’s defenses.

Three of those killed were a 3-year-old boy and his grandparents in the Brovary district outside Kyiv, President Volodymyr Zelensky said. Another person was killed in the Ukrainian capital.

The attack renewed concerns about shortages of Patriot interceptor missiles, which Ukraine relies on to defend against Russian ballistic weapons. Zelensky called for additional international support and tougher sanctions on Moscow as Kyiv seeks permission and assistance to manufacture more interceptors domestically.

Ukraine, meanwhile, carried out long-range drone attacks on oil refineries in Russia’s Krasnodar and Samara regions, according to Ukrainian officials. Kyiv has repeatedly targeted Russia’s energy industry, arguing that it helps finance and supply Moscow’s war effort.