BUCHAREST, Romania (AP) — Romanian authorities said Thursday they found a crater from a suspected drone that may have exploded on impact on its territory near the border with Ukraine, reviving concerns about possible spillover of Russia’s war in Ukraine onto a NATO member country.

The pre-dawn discovery of the crater three kilometers (1.8 miles) west of the village of Plauru, which sits across the Danube River from the Ukrainian port of Izmail, was made after the Romanian Defense Ministry said it detected a series of drones heading towards Ukrainian river ports.

The ministry said the drone had possibly exploded on impact but it was not immediately clear when or from where the drone was launched. An investigation was under way.

“Heinous Russian attacks on Ukraine’s civilian infrastructure had again serious consequences on Romania’s territory,” Foreign Minister Luminita Odobescu wrote on X, the social medial platform formerly known as Twitter, adding that “new evidence of impact was found on Romania’s soil.”

“We call on Russia to stop these war crimes,” she said.

Romanian authorities have previously confirmed drone fragments on its soil in recent weeks, and said the parts resembled those from drones used by the Russian army.

Romanian President Klaus Iohannis called the drone fragment discoveries “an absolutely unacceptable violation of the sovereign airspace of Romania, a NATO ally, with real risks to the security of Romanian citizens in the area.”

The recurring incidents over the past month have left some residents living near the border nervous that the war could spill into their country, and the village of Plauru erected prefabricated concrete shelters for residents last month.

Separately Thursday, the governor of Russia’s Belgorod region on the border with Ukraine said three people, including a child, were killed and two others injured overnight after drone debris fell on a private house, setting it on fire.

The drone was shot down by air defense systems but the debris “effectively destroyed” two private houses on the outskirts of the city of Belgorod, the region’s capital, and damaged several more, said Belgorod Gov. Vyacheslav Gladkov.

The Belgorod region has been a regular target of cross-border shelling and drone attacks. Ukrainian officials have never acknowledged responsibility for attacks on Russian territory.

In Ukraine, the country’s air force said Thursday it intercepted 28 of 33 Shaheed drones that Russia launched overnight across the country. Gov. Oleh Kiper of the southern Odesa region — in which Izmail is located — said Russian forces had targeted Danube port infrastructure in the region, wounding one person.

In recent weeks, Russia has carried out sustained attacks on Ukraine’s Danube ports as part of Moscow’s attempt to disrupt Ukraine’s ability to export grain to world markets.

In the eastern Donetsk region, intense and incessant fighting continued near the city of Avdiivka, said Vitalii Barabash, the head of city’s military administration.

“A very tense situation for the third day. The battles around the city do not cease, and the shelling, both at positions and within the city itself, does not stop,” Barabash said on Ukrainian television.

President Volodymyr Zelenskyy posted on Telegram that “we are holding our ground” in the city. A day earlier, the Ukrainian leader joined a meeting of more than 50 defense leaders from around the world and made a personal pitch for more military aid for his country in the face of the Russian onslaught,

In its latest report, Washington-based think tank Institute for the Study of War said Russian offensive action near Avdiivka is ongoing. Footage from Tuesday and Wednesday showed Russian troops advancing in areas southwest and northwest of the town.

The think tank said such “tactical-level adaptations and successes” by Russian forces were not likely to bring wider operational and strategic gains.

“Avdiivka is also a notoriously well-fortified and defended Ukrainian stronghold, which will likely complicate Russian forces’ ability to closely approach or fully capture the settlement,” it added.

In the northeastern region of Kharkiv, the governor said the death toll from last week’s missile attack that leveled a cafe in the village of Hroza had risen to 56, following the identification of more victims. Gov. Oleh Syniehubov said a 53-year-old woman died after being treated for injuries sustained in the strike.