Happening in Ukraine today: Russian forces seize half of key city as Europe takes action on gas

As European Union nations finally agreed to a partial embargo on Russian oil to punish the Kremlin, Moscow’s forces made gains in eastern Ukraine, establishing positions in nearly half of the key city of Sievierodonetsk.

Meanwhile, two Russian soldiers were sentenced in Ukraine’s second war crimes trial since the beginning of the full-scale Russian invasion.

Here is what you need to know about what’s happening in Ukraine on Tuesday.

1) E.U. leaders cut off ‘huge source of financing’ for Kremlin’s war in Ukraine with a partial ban on Russian oil

In a long-expected move to cut the bloodline of Russia’s war machine, E.U. leaders agreed late Monday to enforce an embargo on most Russian oil imports into the bloc by the end of the year. It’s part of a new package of sanctions against Russia to further hamper its military efforts in Ukraine and to show European unity in the face of the Kremlin’s aggression.

The agreement will immediately impact 75 percent of Russian oil imports, with 90 percent of the Russian oil imported into Europe banned by the year’s end, European Council President Charles Michel said in a tweet.

The embargo covers Russian oil brought in by sea, but allows for an exemption for imports delivered by pipeline after several  E.U. nations heavily reliant on Russian oil voiced opposition to a complete ban.

The Ukrainian foreign ministry said in a statement Tuesday it was “disappointed” that due to resistance from Hungary, in particular, the ban took too long and makes exemptions for pipeline deliveries.

Michel said the sanctions package also includes other “hard-hitting” measures, including keeping Sberbank, Russia’s largest bank, out of the SWIFT global system for financial transfers.

Ukraine has been pushing for an all-out ban on Russian fuels since the early days of the invasion, insisting that the money Moscow continues to receive for its oil and gas is used to kill Ukrainians.

Meanwhile, Russia expanded its gas cuts to Europe on Tuesday with its energy giant Gazprom saying Tuesday it was cutting off deliveries to top Dutch trader GasTerra. Moscow had previously stopped natural gas supplies to Poland, Bulgaria and Finland as the West turned up the pressure of sanctions.

2) Russian forces 'establish positions' in half of key Donbas city

Russian troops have taken positions in half of Sievierodonetsk, a key city in Ukraine’s industrial heartland of the Donbas, a Ukrainian official said Tuesday, as Russia escalated its offensive in the region.

The governor of Luhansk, Sergiy Haidai, said in a series of posts on the Telegram messaging app that the fighting was now taking place in the middle of Sievierodonetsk, and not just on its outskirts.

Later Tuesday, the head of the Sievierodonetsk military administration, Oleksandr Stryuk, said in a television interview that the front line has divided the city in half, but it remained Ukrainian. He said the Russian forces have now “established positions” in half of the city, and communications with those in Sievierodonetsk have been severely disrupted.

Haidai said evacuations of civilians had to be halted amid intensifying fire. He said that 12 buildings in Sievierodonetsk have been damaged in the last 24 hours, and that it is unclear how many civilians have been killed in the last two days.

Sievierodonetsk is the last major city in the Luhansk province that remains under Ukrainian control, and its seizure would boost the Russian offensive in the region, which Moscow has said was its “unconditional priority.”

Russia’s encirclement of Sievierodonetsk and the closure of a pocket around Ukrainian forces in the Luhansk province likely remain its main goal, the British defense ministry said in its daily update. “Progress has been slow but gains are being held,” the ministry said, noting that the Russian forces have been able to secure greater local successes than earlier in their campaign by "massing forces and fires in a relatively small area."

3) A heartbroken mother buries her son twice, as 2 Russian soldiers sentenced in another trial

As Ukraine seeks to ramp up prosecutions for alleged war crimes that it blames on Russian forces, NBC News spoke with a heart-broken mother who had to bury her son twice — once after he was killed by what witnesses said was a Russian tank, and the second time after his remains were exhumed as part of an investigation into his death as a potential war crime.

Olga Kotenko said she didn’t need a prosecutor to tell her that the killing of her son, Volodymyr, was a war crime. But when Ukrainian forces pushed Russian troops out from the Kharkiv region in early May, liberating her village of Vilhivka for the first time in weeks, Kotenko saw an ad on television encouraging people to come forward with information about Russian aggression. She thought it was important to report what happened.

It’s part of Ukraine’s commitment to hold Russian forces accountable for the alleged murder, torture and rape of civilians, even as the conflict is ongoing. The Ukrainian prosecutor general’s office has said it has already documented more than 14,000 crimes of aggression and war crimes and identified more than 600 Russian suspects.

On Tuesday, two captured Russian soldiers were sentenced in Ukraine’s second war crimes trial since the start of the invasion. Alexander Bobikin and Alexander Ivanov both pleaded guilty to artillery attacks on civilian infrastructure in the Kharkiv region last week and were sentenced Tuesday to 11 ½ years in jail each. Their verdicts come just a week after the inaugural case in which a Russian soldier was sentenced to a life sentence for killing an unarmed civilian in northeastern Ukraine.

4) First ship leaves Mariupol port after Russia takes control 

The first ship has left the port city of Mariupol since Russia took full control after months of siege and resistance by remnants of Ukraine’s defense, according to a separatist leader and an Ukrainian official.

The head of the so-called Donetsk People’s Republic, Denis Pushilin, said in a Telegram post that the port had resumed operations Tuesday after its structures and waters were demined, and that the first ship, carrying 2,500 tons of steel sheets, has departed for the Russian city of Rostov-on-Don.

The ship’s departure, cargo and destination were also confirmed by Petro Andryushchenko, adviser to the city’s mayor.

Meanwhile, Kirill Stremousov, the deputy head of the so-called military-civilian administration of the neighboring Kherson region installed by Russia, said the port could be used to ship grain from the Kherson region to Russia, Interfax reported. Ukraine has blamed Moscow for stealing grain from its occupied territories to be transported to Russia or sold elsewhere.

Mariupol has been heavily shelled during months of fighting, leaving its residents with no access to food, water or electricity. Its last Ukrainian defenders surrendered earlier this month, leaving the city completely in Russian hands.

5) Biden says U.S. will not send 'rocket systems that can strike into Russia' 

Washington will not supply Kyiv with rocket systems that can reach into Russia, President Joe Biden told reporters Monday, amid calls by Ukraine for more advanced weapons as it tries to contain Russian advances in the Donbas.

Biden’s comments come amid reports suggesting this only rules out providing certain long-range munitions and that Washington may still be gearing up to send advanced, long-range rocket systems to Ukraine. It was unclear whether anything had changed.

Dmitry Medvedev, the deputy chairman of the Russian Security Council who is also a former president, called Biden’s comments “reasonable,” saying in a post on Telegram that Russia could attack cities “well outside Kyiv” if its own cities were targeted.

Meanwhile, the newly appointed U.S. ambassador to Ukraine, Bridget Brink, arrived in Kyiv on Monday in a sign of diplomatic support as the U.S. is re-establishing its presence on the ground after evacuating diplomatic staff amid fears of invasion.

“Honored to join our fantastic team at [the U.S. Embassy in Kyiv] as we stand with Ukraine,” she tweeted along with a photo of herself in the Ukrainian capital.