A joint statement from Foreign Minister Dmytro Kuleba and Defence Minister Oleksiy Reznikov came on the eve of a major donor meeting to be hosted by the United States at the Ramstein military base in Germany.

"We appeal to all partner states that have already provided military assistance or are planning to provide it with a call to considerably reinforce their practical contribution to strengthening Ukraine's ability to defend itself," Kuleba and Reznikov said in the statement.

They said Russia "retains a substantial quantitative advantage in troops, weapons and military equipment" and that the Kremlin is "determined to further escalate hostilities".

The supply of modern armoured vehicles is "one of the most pressing and urgent needs," the ministers said.

The statement also said they "welcome the bold and very timely decision" of Britain -- the first Western nation to pledge heavy tanks to Ukraine -- to supply Challenger tanks but added, "it is not sufficient to achieve operational goals".

They called on a dozen countries that have the advanced Leopard battle tanks, including Germany, Poland and Turkey, to send them to Ukraine.

"We guarantee that we will use these weapons responsibly and exclusively for the purpose of protecting the territorial integrity of Ukraine within internationally recognised borders," they said.