Seven crew members disappeared after the drone attack and the tanker was set on fire off the coast of Romania
Search and rescue operations are underway in the Black Sea after the latest attack in the area.
Romanian navy officials say seven of the 12 crew members are missing after a drone strike set a chemical tanker on fire off the coast of Romania.
The San Marino-flagged wine merchant was 13 nautical miles (24 km) east of the mouth of the Danube at Solina when it reported the explosions and fire.
The Wine Trader and another chemical tanker in the region, the Yara J, were both hit by drones on Wednesday, Romanian President Nicosor Don confirmed.
The wine merchant was empty of cargo at that time.
Moscow announced that two cargo ships with military cargo bound for the Ukrainian port of Odessa were hit. He did not name the ships.
During the night, a swarm of Russian drones was detected not far from the scene, near Ukraine's Serpent Island.
The western coast of the Black Sea has recently seen a flood of drone attacks.
On Tuesday, two commercial ships were hit by drones off the southern coast of Romania's neighbor Bulgaria, sinking one and leaving 11 crew members missing.
Bulgaria summoned the country's envoy and said that Russia was behind the attack.
Romanian authorities announced that the search and rescue operation for the missing members of the wine merchant is continuing. Two Blackhawk helicopters and two rescue boats have been deployed.
The Romanian Interior Ministry has released a video showing one of the helicopters hovering above the float.
The priority right now is to get the four crew members confirmed alive while ensuring the safety of rescue teams with extremely high waves reported in the area.
The tanker Wine Trader, which was sailing from Tunisia to Romania, reported several explosions around 07:00 (05:00 GMT).
Romanian media quoted crews of nearby ships as saying that the wine merchant was hit by two drones.
The leaders of Romania and Bulgaria are soon to discuss invoking Article 4 of the NATO treaty.
It allows each member of the military alliance to seek advice from its allies if it believes its territorial integrity or security is at risk.
The President of Romania said: We want to have all the information about what happened, but the answer will be from the Romanian government.
Dan is due to meet NATO Secretary General Mark Rutte alongside Bulgarian Prime Minister Roman Radev in Brussels to discuss the growing security threats in the Black Sea region.
The Romanian president said discussions would focus on operational requirements, including additional equipment to protect shipping in the region.
Ukraine has directly blamed Russia for previous attacks on civilian vessels on the western side of the Black Sea - a key route for Ukrainian exports and imports.
On Tuesday, Ursula von der Leyen, president of the European Commission, spoke of the Black Sea becoming "another front for the escalation of Russia's war in Ukraine." This is unacceptable.
The Russian military has recently stepped up its attacks on ships in the region as part of its war against Ukraine.
A fire broke out on the Comoros-flagged Yara J late Wednesday after it was hit by a drone, but its crew - who are reportedly safe - were able to put out the flames themselves.
Last week, two more ships were hit off the coast of Bulgaria, and on the same day, Ukraine hit an oil tanker in the Russian port of Sochi in the Black Sea.
Moscow says it is targeting ships delivering weapons and dual-use cargo to Ukrainian ports.
Kiev and its European allies say commercial ships carrying grain and other civilian cargo are being attacked.
Russia and Ukraine are both major grain exporters, and Turkey has called on both countries to stop attacks in the Black Sea.
Moscow has repeatedly rejected US and European requests for a maritime ceasefire in the Black Sea and blames Ukraine for attacking Russian commercial ships in the region.
Russian President Vladimir Putin launched a full-scale invasion of Ukraine in 2022, and Moscow currently controls about 20 percent of Ukraine's territory.