BOBRYK, Ukraine (AP) -- As uncertainty in U.S.-Ukraine relations grows, informal ties with some U.S. philanthropists built over three years of war with Russia are holding firm.

One such benefactor is Howard G. Buffett, a Republican and son of billionaire investor Warren Buffett. He's making his 18th visit to Ukraine since Russia's full-scale invasion of Ukraine in 2022. The trip comes as the new U.S. administration led by President Donald Trump is trying to broker a temporary ceasefire between Russia and Ukraine. But the fighting has continued, and it remains unclear whether the United States will maintain its support for Ukraine in repelling Russia's invasion.

"It doesn't change anything we do. We're on track," Buffett told The Associated Press, adding that his foundation will surpass $1 billion in aid to Ukraine this year. He called the prospect of a peace deal "impossible."

"Putin doesn't want it, and he won't respect it," he said. "There's no easy way to end the war. So, we'll stick with it as long as we need to."

The AP caught up with Buffett aboard a train with Ukraine's Economy Minister Yuliia Svyrydenko on Saturday. Their shared commitment to humanitarian demining brought them together in 2023, and they've remained in close contact since then. Svyrydenko calls him "one of the greatest friends of Ukraine."

Buffett is among a number of Americans across the U.S. political spectrum who support Ukraine's war effort, either through financial aid or volunteer military service, who say the U.S. hasn't done enough to help Ukraine defeat Russia over the past few years.

On this trip, Buffett and Svyrydenko traveled to the country's northern Sumy region, where the situation has significantly worsened following Ukrainian forces' loss of ground in Russia's Kursk region.

They visited the villages of Popivka and Bobryk, which -- like much of the region -- lie in a high-risk zone for land mines. Parts of the area were occupied by Russian forces in 2022 and are now considered potentially contaminated. They also stopped at a local school that had been relocated to a basement, where children now study during hours-long air raid alerts.

Buffett's foundation, which focuses on humanitarian needs like agriculture, infrastructure and mine clearance, has contributed about $800 million to Ukraine since the start of the full-scale invasion, including $175 million in humanitarian demining. Svyrydenko's ministry is responsible for Ukraine's humanitarian demining infrastructure.

"He understands very well that if a country that can feed 400 million people cannot clear its fields and loses at least $12 billion of GDP every year due to mined land, it's a major challenge," Svyrydenko said of Buffett.

According to Ukraine's Ministry of Economy, the country's agricultural sector has lost 20.5% of its farmland since the invasion -- due to land mines, occupation and ongoing fighting.

Roughly 139,000 square kilometers (53,670 square miles) of Ukrainian land -- about the size of the state of New York -- are potentially mined. Two-thirds of that territory consists of fertile farmland where generations of Ukrainians have grown wheat.

Since the beginning of the war, 335 people have been killed and 823 wounded in mine-related incidents. An estimated 6.1 million people live in areas considered at risk of landmine contamination.

Despite rocky relations and growing uncertainty in the United States, Buffett said he believes many U.S. lawmakers still support the principles of freedom and democracy and won't abandon Ukraine as it fights for its sovereignty.

"At the end of the day, I think the U.S. will do the right thing, but it may be a painful process and there may be a lot more Ukrainians that die," he said.

The Buffett Foundation funded several bipartisan U.S. congressional delegations to Ukraine in 2023 and plans to bring another group in May.

Buffett, whose foundation has worked in conflict zones for over two decades, said witnessing the conditions firsthand is critical to understanding the war's scale. He recalled one drive in particular -- from Kharkiv to Borova, near the front line --where he passed through village after village flattened by Russian attacks.

He added that atrocities committed in towns like Bucha, Borodyanka and Irpin, where Russian forces were accused of torturing, raping and executing civilians, are often forgotten outside Ukraine.

"That's why showing up matters. Hearing it from the people living it is the only way to truly understand."