The United States still strongly supports Ukraine's claim on the Crimean peninsula.

US Vice President Mike Pence delivers a speech at a ceremony marking the 80th anniversary of the outbreak of World War II in Poland on September 1. Photo: Reuters

Speaking ahead of a bilateral meeting with Ukrainian President Volodymyr Zelenskiy in Warsaw, Poland, Pence did not address reports that Trump was considering cutting $250 million in military aid to the country. However, he asserted that the relationship between the two countries was stronger than ever.

“We will continue to stand with the Ukrainian people on issues of security, sovereignty, and unity, including Ukraine's legitimate rights in Crimea,” the US Vice President said.

Washington is a key ally of Kiev, having imposed sanctions on Russia over its annexation of Crimea and support for pro-Moscow separatists in eastern Ukraine.

However, Mr Trump, who has close ties to Russian President Vladimir Putin, believes any aid money must be justified and is reviewing the move before the end of the fiscal year on September 30.

Last month, he abandoned an effort to reduce billions of dollars in foreign aid, after Congress criticized it as an attempt to override lawmakers' authority over government spending.

Pence’s “vote of confidence” resonated with statements from US National Security Adviser John Bolton, who met with Mr Zelenskiy last week in Kiev and confirmed that restoring Ukraine’s sovereignty over the Crimean peninsula and the Donbass region was on the table.

According to Reuters, the conflict in Donbass between the Ukrainian army and Russian-backed separatists has killed 13,000 people in the past five years.

Pence and Zelenskiy reportedly traveled to Warsaw to attend a memorial service marking the 80th anniversary of the outbreak of World War II.