Earlier on Wednesday, Russia's former president Dmitry Medvedev suggested that Ukraine may not exist in two years.
"I saw a report that Ukraine wants to receive LNG (liquified natural gas) under a lend-lease agreement from its overseas masters with payment for delivery in two years," Medvedev, who is now deputy head of the Security Council, wrote on Telegram.
"And who said that in two yeas Ukraine will even exist on the world map?" said the close ally of President Vladimir Putin.
The Ukrainian president has appealed for heavy weapons from the West, criticising the "restrained behaviour" of some European leaders which he said had "slowed down arms supplies very much".
"I am grateful for what is coming, but it must come faster," he told Danish journalists in an online briefing on Tuesday.
The United States and Britain have said they are providing Kyiv with long-range precision artillery batteries, defying warnings from the Kremlin.
