Rescuers were searching for seven missing crew on Thursday from one of ‌two chemical tankers that caught fire overnight inside Romanian territorial waters in the Black Sea, after Russian drones strayed into Romanian airspace, Romanian officials said.

Romanian officials stopped short of explicitly linking the fires onboard the ships to the Russian drones.

But the incidents follow drone strikes on at ​least five other cargo ships near the coasts of Romania and neighboring fellow NATO member Bulgaria over the past ​10 days.

At least 23 sailors were lost from those strikes, which unlike the latest incidents ⁠took place just outside NATO’s territorial waters.

The two ships hit overnight were both anchored in the Black Sea near the ​mouth of the canal leading into the Danube River, a major shipping route used by Ukraine as Russia has attacked Ukraine’s own ​Black Sea ports.

Romania’s naval authority said it received an emergency alert from the San Marino-flagged tanker Wine Trader.

Seven of its 12 crew were missing and 5 were rescued.

The interior ministry said it had sent two Black Hawk helicopters to the search and rescue mission, as well as ​two ships with medical staff on board.

“At the moment, the rescue cannot be done safely because of very big waves,” it ​said in a statement.

Late on Wednesday, the Comoros-flagged chemical and oil tanker Yara J also caught fire.

Romanian authorities initially said it was not ‌clear whether ⁠it had been attacked. All its crew were safe.

Romania shares a 381-mile border with Ukraine, much of it along the Danube. It has reported repeated breaches of its airspace by Russian drones over the past four years.

Both Wine Trader and Yara J caught fire near the mouth of the Danube River’s Sulina Canal leading to the Black Sea, where ships often anchor waiting to pass ​because of delays from weather ​and congestion.

Increasing attacks on Black ⁠Sea shipping connected with the Russia-Ukraine war in recent months have threatened to cause a global food crisis, as both countries are major exporters of grain, as is Romania.

“We’re looking at the Black ​Sea as a global food artery,” Romanian Foreign Minister Oana Toiu told a security conference ​in Warsaw earlier ⁠this week.

“It is currently, unfortunately, the deadliest sea when it comes to the number of casualties of sailors in the last months. That means we need to increase our investments in deterrence, defence.”

Bulgarian Prime Minister Rumen Radev said EU leaders would discuss on Thursday a ⁠proposed moratorium on ​attacks on civilian ships in the Black Sea.

Russia has been bombing Ukraine’s ​Black Sea ports, forcing Kyiv to rely increasingly on Danube River ports and shipping routes close to the coasts of Bulgaria and Romania.

For its part, ​Ukraine has targeted Russian ships near the mouth of the Don River in the Azov Sea.