KYIV, Ukraine (NewsNation) — Russian forces continued to seize key parts of Ukraine Wednesday, prompting the U.S. to officially allege war crimes by Russia.

“Our assessment is based on a careful review of available information from public and intelligence sources,” Secretary of State Antony Blinken said in a statement. “As with any alleged crime, a court of law with jurisdiction over the crime is ultimately responsible for determining criminal guilt in specific cases.”

“Every day that Russia’s forces continue their brutal attacks, the number of innocent civilians killed and wounded, including women and children, climbs,” he continued, adding that Russian President Vladimir Putin has unleashed “unrelenting violence that has caused death and destruction across Ukraine.”

Ukrainian leaders accused Russia of seizing 15 rescue workers and drivers from a humanitarian convoy trying to get needed food and other supplies into the hard-hit city of Mariupol. Ukrainian President Volodymyr Zelenskyy accused Russian forces of blocking the aid convoy despite agreeing to the route ahead of time.

“We are trying to organize stable humanitarian corridors for Mariupol residents, but almost all of our attempts, unfortunately, are foiled by the Russian occupiers, by shelling or deliberate terror,” Zelenskyy said.

He said Mariupol is being “reduced to ashes” as an estimated 100,000 civilians remain in the city. Before the war, 430,000 people lived in Mariupol.

Wednesday night, Zelenskyy noted the passing of a full month since the invasion began with a video address.

“We all must stop Russia,” the caption to the address said. “The world must stop the war. I thank everyone who acts in support of Ukraine. In support of freedom. But the war continues. The acts of terror against peaceful people go on. One month already! That long! It breaks my heart, hearts of all Ukrainians and every free person on the planet. That’s why I ask you to stand against the war!”

On Wednesday, the Ukrainian National Guard’s Special Forces Unit released a drone video showing the widespread destruction of Mariupol, with smoke rising from some buildings in the burned-out city. Soot and ash cover the ground and buildings stretching to the Sea of Azov.

American intelligence says Russian ships in the sea of Azov are now joining in the bombardment of the city. The official said there were about seven Russian ships in that area, including a minesweeper and a couple of landing vessels.

Addressing Japan’s Parliament on Wednesday, Zelenskyy said four weeks of war have killed thousands of people and 121 of Ukraine’s children.

“Our people cannot even adequately bury their murdered relatives, friends and neighbors, they have to be buried right in the yards of destroyed buildings, next to the roads,” he said.

In the meantime, President Joe Biden is headed to Europe for an emergency NATO summit Thursday on Russia’s invasion and increasingly hostile stance toward the West, where NATO members and other European allies are strengthening their defenses.

Biden is traveling to Brussels and Poland, which has received more than 2 million Ukrainian refugees since the Feb. 24 invasion.

He is expected to seek continued unity among Western allies and to announce more sanctions on Russia. One of the options Biden is considering, according to a U.S. official who spoke on the condition of anonymity, is to target hundreds of members of Russia’s lower house of Parliament.

On the eve of their summit meeting with Biden, European Union nations signed off on another 500 million euros ($550 million) in military aid for Ukraine.

Ursula von der Leyen, head of the European Union’s executive arm, said she will discuss with Biden the possibility of securing extra deliveries of liquefied natural gas from the U.S. for the 27-nation bloc.

In the U.S. on Wednesday, Treasury Secretary Janet Yellen was set to meet with lawmakers to discuss a possible freeze on Russian reserves of gold.

Kremlin spokesman Dmitry Peskov told CNN that Putin has yet to achieve all he wants in Ukraine. He insisted that the military operation was going “strictly in accordance with the plans and purposes that were established beforehand.”

Putin’s aims remain to “get rid of the military potential of Ukraine” and to “ensure that Ukraine changes from an anti-Russian center to a neutral country,” Peskov said.

In Ukraine’s capital, Kyiv, continued shelling and gunfire shook the city early Wednesday, with plumes of black smoke rising from the western outskirts.

Russian news outlet The Insider announced Oksana Baulina, a Russian journalist, was killed while documenting the damage done by the shelling in Kyiv. A civilian also died, and so were two people accompanying Baulina.

Russian forces also bombed and destroyed a bridge in the encircled northern city of Chernihiv that crossed the Desna River and connected the city to Kyiv, regional governor Viacheslav Chaus said Wednesday. Deliveries of humanitarian aid and evacuations of civilians went through that bridge. Local authorities have warned of a humanitarian disaster in the city, with no water or electricity.

Still, Ukrainians are continuing to fight.

“We have seen indications that the Ukrainians are going a bit more on the offensive now,” Pentagon spokesman John Kirby said. He said that was particularly true in southern Ukraine, including near Kherson, where “they have tried to regain territory.”

The U.S. estimates Russia has lost a bit more than 10% of the overall combat capability it had at the start of the fight, including troops, tanks and other materiel. Western officials say Russian forces are facing serious shortages of food, fuel and cold weather gear, leaving some soldiers suffering from frostbite.

The invasion has driven more than 10 million people from their homes, almost a quarter of Ukraine’s population, according to the United Nations.

NATO estimated Wednesday that 7,000 to 15,000 Russian soldiers have been killed in a month of fighting in Ukraine, with anywhere from 30,000 t 40,000 battlefield casualties in total. A senior NATO military official said the estimate was based on information from Ukrainian officials, what Russia has released, and intelligence gathered from open sources.

The official spoke on the condition of anonymity under ground rules set by NATO.

Talks to end the fighting have continued by video. Zelenskyy said negotiations with Russia are going “step by step, but they are going forward.”

U.N. Secretary-General Antonio Guterres said he saw progress “coming into view on several key issues,” and that the gains are enough to end hostilities now. He gave no details.

However, he said that there were no signs Moscow was ready to compromise.

But not all Ukrainians agree with the plan to negotiate. Ukrainian Parliament member Kira Rudik talked to “The Donlon Report” on Wednesday and said talks with Russia should be off the table altogether.

“I do not believe we can cut a deal with Putin because he’s known for not keeping his word and Russia is known for not honoring any kind of deals,” Rudik said. “I don’t believe we should agree on anything with them. I don’t think anything can end this.”

Mariupol is a crucial port for Ukraine and lies along a stretch of territory between Russia and Crimea. The siege has cut the city off from the sea and allowed Russia to establish a land corridor to Crimea.

In their last update March 15, Mariupol officials said at least 2,300 people had died in the siege. Accounts from the city suggest the true toll is much higher, with bodies lying uncollected. Airstrikes over the past week destroyed a theater and an art school where many civilians were taking shelter.

The Associated Press contributed to this report.