UZHHOROD, Ukraine (NYTIMES) - Jill Biden, the US first lady, travelled to western Ukraine in an unannounced trip on Sunday (May 8), the latest show of support from the United States, which in recent weeks has significantly increased military aid for Ukraine and sent others close to President Joe Biden into the country.

Jill Biden met Ukraine's first lady, Olena Zelenska, at a school converted to assist refugees who had come from other parts of the country to Uzhhorod, a town of 100,000 people a few kilometres from the border with Slovakia. Zelenska, wife of President Volodymyr Zelensky, had not been seen in public since Russia's invasion began on Feb 24.

"I thought it was important to show the Ukrainian people that this war has to stop, and this war has been brutal," Biden told reporters as she sat at a table across from Zelenska, "and that the people of the United States stand with the people of Ukraine."

Biden made her trip on a day of public displays of support for Ukraine, with visits from Bono and Prime Minister Justin Trudeau of Canada, and as rescuers searched for survivors from a Russian airstrike on a school in the east that officials feared had left dozens dead. In Kyiv, a team of senior American diplomats returned to the US Embassy for the first time since Russia invaded Ukraine, a move that coincided with Victory in Europe Day.

The day was a patchwork of the hopeful and the foreboding. Her visit also came as Western officials were bracing for the possibility that Russian President Vladimir Putin might use his country's Victory Day holiday, which fell on Monday, as a reason to intensify attacks on Ukrainian citizens.

Ukrainian officials understand the emotional power of social media and headlines written by the Western press and have invited an assortment of Western officials - and Bono - into the country in recent days. They reached out several days before Biden's planned four-day tour of Eastern Europe to suggest a meeting with Zelenska in Ukraine, according to Michael LaRosa, the first lady's spokesman.

Such a high-stakes visit is a rarity for any sitting first lady; they do not usually visit war zones, and the last one to travel to one alone was Laura Bush, who visited Afghanistan in 2008.

Biden, an English professor who teaches full time, has so far spent much of her time as first lady travelling the United States, urging Americans to take vaccines and support community colleges, or touting Joe Biden's plans for social spending.

Until now, she has had comparatively little to say about Ukraine, but her full-throated call for an end to the war on Sunday was a departure that reflected the bolder and broader steps the Biden administration has taken to move against Russian aggression without engaging Moscow in an all-out war.

It also appeared to be an opportunity for the first lady - who, like many before her, has positioned her identity as a mother as a central one - to use her office to highlight the reality of the war in Ukraine: As many as 90 per cent of the people who have been displaced are women and children, according to United Nations figures.

Zelenska, 44, was among the first to be displaced when the war began.

In a speech only days after the first Russian missiles fell on Kyiv, Ukraine's capital, Zelensky said he knew he was the first target for assassination in case of an occupation. His wife and children, Oleksandra, 17, and Kyrylo, 9, he said, are "target No. 2". Since then, her whereabouts has been kept private.

A first lady who once focused on issues of female empowerment, literacy and culture in Ukraine, Zelenska, like her husband, now spends much of her time trying to bring the world's attention to what is happening in her country. She wrote to Biden in April, expressing her concerns for the emotional well-being of the citizens of Ukraine, LaRosa said.

Her concerns appeared to have been received by Biden, who spent much of her time in front of the cameras quizzing humanitarian organisation workers on their capacity to support women and children who had endured the trauma of war.

At stop after stop, in Romania and in Slovakia and later in Ukraine, Biden talked to children who had circles of exhaustion under their eyes and mothers who were on the verge of tears. She stood among bottles of baby formula and well-worn toys and asked whether volunteers had what they needed.

Allida Black, a historian who studies first ladies, said Biden's work was in the tradition of other first ladies who had travelled oversees to witness the "personification of pain", hearing stories of trauma and war, all while staying within the limits of an unelected role within the administration.

"There's real finesse to this," said Black, who has been an adviser to Hillary Clinton. "Because you've got to carry all of those memories with you. It's hard work."

Before stopping in Ukraine on Sunday, Biden travelled to the Slovakian city of Kosice, where she met with refugees at a bus station that had been converted to assist new arrivals to the country.

There a woman named Viktozie Kutocha clutched her daughter, Yulie, and told the first lady that she struggled to explain to her child what had happened to their lives.

"How I can explain this to child? It's impossible," she said. "I try to keep them safe. It's my mission."

"It's senseless," Biden said.

After crossing the border into Ukraine, she was driven for about 15 minutes to the carpark of a school building. Zelenska quietly slipped out of a vehicle to greet her.

The two women exchanged hugs and, later, Zelenska thanked Biden for making a "courageous" visit.

"We understand what it takes for the US first lady to come here during a war, where the military actions are taking place every day, where the air sirens are happening every day, even today," she told Biden.

The visit made Biden the latest high-profile person close to Joe Biden to travel to Ukraine. Secretary of State Antony Blinken and Defence Secretary Lloyd Austin visited Kyiv last month, and House Speaker Nancy Pelosi met with Zelensky there last week.

Joe Biden travelled to Poland for three days at the end of March. While he visited troops near the border with Ukraine, he stopped short of entering the country because of security concerns.