Romanian President Nicusor Dan blamed Russia for an attack on a merchant vessel in the Black Sea on Friday morning.
A drone strike sank the merchant ship, with 13 Ukrainian and Azeri crew members on board, near Romanian territorial waters.
The attack killed at least 1 sailor, and three others were still missing, according to Dan.
Nine of the 13 crew members have been rescued.
Attack on merchant shipping on the rise in the Black Sea: What to know
The drone strike on the ship, called Khoryv, is believed to be the fourth merchant vessel to have been attacked off the coast of Romania this month.
Two weeks ago, two merchant vessels were also set ablaze in the western Black Sea, which is a vital shipping corridor heavily used by Ukraine.
One of those ships was inside Romanian territorial waters. Romania raised concerns about Russian provocation in waters at the edge of or controlled by NATO members.
That's because Bulgaria, also a NATO member like Romania, has raised similar concerns too.
Bulgaria has raised concerns about Russian strikes having edged too close to its exclusive economic zone in the Black Sea after merchant ships were hit by drones earlier this month too.
Both Romania and Bulgaria have blamed Russia for the attacks and have called on the alliance to do more to protect commercial shipping in the Black Sea.
NATO said earlier this week that it was sending more maritime patrol aircraft and radar systems to the Black Sea without having blamed any country for the attacks there.
About 23 sailors had been reported dead or missing in incidents in the Black Sea in the 10 days leading up to October 15, according to Reuters.
That tally is higher now.
Ursula von der Leyen, the president of the European Commission, condemned the increasing attacks on vessels in the Black Sea too, earlier this month calling it "unacceptable" that "the Black Sea has become another front of escalation of the Russian war in Ukraine."
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Edited by: Sean Sinico
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