KYIV, Ukraine >> Moscow promised retaliation Saturday after Ukrainian drones hit a Russian tanker in the Black Sea near Crimea late Friday, the second sea attack involving drones in one day.

Ukraine struck a major Russian port earlier on Friday.

Moscow strongly condemned what it sees as a Ukrainian “terrorist attack” on a civilian vessel in the Kerch Strait, said Russian Foreign Ministry spokeswoman Maria Zakharova.

“There can be no justification for such barbaric actions, they will not go unanswered and their authors and perpetrators will inevitably be punished,” she wrote on the Telegram messaging app.

As Kyiv’s naval capabilities grow, the Black Sea is becoming an increasingly important battleground in the war.

Three weeks ago, Moscow withdrew from a key export agreement that allowed Ukraine to ship millions of tons of grain across the Black Sea for sale on world markets. In the wake of that withdrawal, Russia carried out repeated strikes on Ukrainian ports, including Odesa.

An official with Ukraine’s Security Service confirmed to The Associated Press that the service was behind the attack on the tanker, which was transporting fuel for Russian forces. A sea drone, filled with 450 kilograms (992 pounds) of TNT, was used for the attack, added the official, who spoke on condition of anonymity because he was not authorized to give official statements.

“The Sig tanker … suffered a hole in the engine room near the waterline on the starboard side, presumably as a result of a sea drone attack,” Russia’s Federal Agency for Marine and River Transport wrote on Telegram, adding that there were no casualties among the 11 crew members.

Vladimir Rogov, a Kremlin-installed official in Ukraine’s partially occupied southern Zaporizhzhia region, said several members of the ship’s crew were wounded because of broken glass.

Without specifying that Ukraine was responsible for the drone strike, Vasyl Malyuk, who leads Ukraine’s Security Service, said that “such special operations are conducted in the territorial waters of Ukraine and are completely legal.” Any such explosions, he said, are “an absolutely logical and effective step with regard to the enemy.”

The attack briefly halted traffic on the Kerch Bridge, as well as ferry transport.

Tugboats were deployed to assist the tanker, which is under United States sanctions for helping provide jet fuel to Russian forces fighting in Syria, according to Russia’s Tass news agency.

Ukraine’s earlier strike on Novorossiysk halted maritime traffic for a few hours and marked the first time a commercial Russian port has been targeted in the nearly 18-month-old conflict. The port has a naval base, shipbuilding yards and an oil terminal, and is key for exports. It lies about 110 kilometers (about 60 miles) east of Crimea.

Shipping expert Jayendu Krishna told The Associated Press that the attacks left Russian shipping activity “largely unaffected.” He believes that they may increase the risk of Russian attacks on Ukrainian ports rather than serving as a tool to put pressure on Russia to halt attacks and reinstate the grain deal.

“Every time anything happens to Russia, you see Putin in retaliation mode … therefore, you may see further attacks on other parts of Ukraine,” Krishna said.

“I think it will probably compound the effect and compound the risk in the Black Sea, rather than reducing it,” he added. “It’s very difficult for me to imagine that Russia will give in, unless and until their banks have smooth operations, and they’re able to export their own cargo uninterruptedly.”

A Telegram post on Saturday by Deputy Chair of Russia’s Security Council Dmitry Medvedev implied that Russia would increase its attacks against Ukrainian ports in response to Kyiv’s attacks on Russian ships in the Black Sea:

“Apparently, the strikes on Odesa, Izmail, and other places were not enough for them,” he wrote.

In other developments, Russia’s Defense Ministry said Saturday it captured a settlement in Ukraine’s easternmost Luhansk region, most of which is occupied by Russia. “In the area of Kupiansk … the settlement of Novoselivske was liberated,” the ministry wrote on Telegram.

Elsewhere, a two-day summit on finding a peaceful settlement to the war kicked off in Saudi Arabia.

Senior officials from around 40 countries — but not Russia — will aim to agree key principles on how to end the conflict.

“It is very important because in such matters as food security, the fate of millions of people in Africa, Asia, and other parts of the world directly depends on how fast the world will be in implementing the Peace Formula,” Ukrainian President Volodymyr Zelenskyy said of the summit. “I am grateful to Saudi Arabia for this platform for negotiations.”

The main Ukrainian envoy to the summit in Jeddah, chief Ukrainian presidential aide Andriy Yermak, spoke of the talks on Friday night in a television interview published on his Telegram account: “I expect that the conversation will be difficult, but behind us is truth, behind us goodness,” he said.

Commenting on the talks in Saudi Arabia, Zakharova told Russian state media that the idea of making decisions on the conflict without the participation of Moscow was “absurd.” Nevertheless, she said, delegates have “full scope for creativity” to discuss the issue.