(NewsNation) —  A senior U.S. official said Russia has appointed a new commander to oversee its war on Ukraine.

The official speaking on condition of anonymity said Russia has turned to Gen. Alexander Dvornikov, 60, one of Russia’s most experienced military officers and — according to U.S. officials — a general with a record of brutality against civilians in Syria and other war theaters. 

The White House national security adviser, Jake Sullivan, told CNN on Sunday that “this general will just be another author of crimes and brutality against Ukrainian civilians.” And he said “no appointment of any general can erase the fact that Russia has already faced a strategic failure in Ukraine.”

Ukraine said on Sunday it was seeking another round of European Union sanctions against Moscow and more military aid from its allies as Russian forces destroyed an airport and other targets in the east of the country.

Russia has failed to take any major cities since it launched its invasion on Feb. 24, but Ukraine says it has been gathering its forces in the east for a major assault and has urged people to flee.

Experts say a full-scale offensive in the east could start within days, though questions remained about the ability of Russia’s depleted and demoralized forces to conquer much ground after Ukraine’s inspired defenders repelled their push to capture the capital, Kyiv.

Russia has pulled its troops from the northern part of the country and refocused on the eastern Donbas region, where Moscow-backed separatists have fought Ukrainian troops for eight years and controlled some territory before the war, now in its 46th day.

The Ukrainian military command said Sunday that the Russian troops have continued attempts to break Ukrainian defenses near Izyum, southeast of Kharkiv. It reported that Russia was sending reinforcements to Izyum while continuing the shelling of Kharkiv.

New satellite imagery released by Maxar Technologies shows a military convoy moving through Velykyi Burluk in Ukraine’s Kharkiv Oblast.

Maxar Technologies said the convoy was “at least eight miles long” and consisted of hundreds of vehicles, including armored vehicles, trucks with towed artillery, and support equipment.

Ukrainian Armed Forces said Russian troops were attempting to gain access to the city of Izyum in eastern Ukraine.

On Sunday, Russian forces shelled Kharkiv, Ukraine’s second-largest city, in the northeast and sent reinforcements toward Izyum to the southeast in an attempt to break Ukraine’s defenses, the Ukrainian military command said. The Russians also kept up their siege of Mariupol, a key southern port that has been under attack and surrounded for nearly 1 and a half months.

However, Western assessments expressed increasing confidence in the ability of Ukraine’s defenders to repel Russian assaults, portraying Russia’s troops as suffering from low morale and mounting casualties.

Britain’s Defense Ministry said Sunday that the Russian military was seeking to respond to mounting losses by boosting troop numbers with personnel who have been discharged from military service since 2012.

In an update on Twitter, the ministry also said that the Russian military’s efforts to “generate more fighting power” also include trying to recruit from Trans-Dniester, a breakaway region in Moldova that borders Ukraine.

Several European leaders have made efforts to show solidarity with battle-scarred Ukraine. President Volodymyr Zelenskyy thanked the leaders of Britain and Austria for their visits to Kyiv on Saturday and pledges of further support.

He also thanked the European Commission president and Canada’s prime minister for a global fundraising event that brought in more than $11 billion for the millions of Ukrainians who have fled their homes.

Zelenskyy repeated his call for a complete embargo on Russian oil and gas, which he called the sources of Russia’s “self-confidence and impunity.” Some European countries depend heavily on imported Russian energy.

He also acknowledged that peace likely will not come quickly. Talks so far have not included Russian President Vladimir Putin or other top officials.

“We have to fight, but fight for life. You can’t fight for dust when there is nothing and no people. That’s why it is important to stop this war,” the president said.

 Pope Francis opened Holy Week Sunday with a call for an Easter truce in Ukraine to make room for a negotiated peace, highlighting the need for leaders to “make some sacrifices for the good of the people.”

Celebrating Palm Sunday Mass before crowds in St. Peter’s Square for the first time since the pandemic, Pope Francis called for “weapons to be laid down to begin an Easter truce, not to reload weapons and resume fighting, no! A truce to reach peace through real negotiations.”

Ukrainian authorities have accused Russia forces of committing war crimes against thousands of civilians during the invasion, including airstrikes on hospitals, a missile attack that killed 57 people at a train station Friday and shooting residents of towns in the north at close range.

Graphic evidence of civilian slayings emerged after Russian forces withdrew from Bucha, and firefighters were searching buildings in Borodyanka, another settlement outside Kyiv. Russia has denied engaging in war crimes and falsely claimed that the scenes in Bucha were staged.

Ukrainian authorities have said they expect to find more mass killings once they reach the southern port city of Mariupol, which is also in the Donbas and has been subjected to a monthlong blockade and intense fighting. The city’s location on the Sea of Azov is critical to establishing a land bridge from the Crimean Peninsula, which Russia seized from Ukraine eight years ago.

Ukrainian officials have pleaded with Western leaders to send more arms and further punish Moscow with sanctions, including the exclusion of Russian banks from the global financial system and a total EU embargo on Russian gas and oil.

During his visit Saturday, Austrian Chancellor Karl Nehammer said he expects more EU sanctions against Russia, but defended his country’s opposition so far to cutting off deliveries of Russian gas.

British Prime Minister Boris Johnson’s visit came a day after the U.K. pledged an additional 100 million pounds $130 million in high-grade military equipment. Johnson also confirmed further economic support, guaranteeing an additional $500 million in World Bank lending to Ukraine, taking Britain’s total loan guarantee to up to $1 billion.