Russia's Vladimir Putin on Wednesday praised Ukrainian leader Volodymyr Zelensky as "likeable" before the two faces off at a summit on the conflict in eastern Ukraine.

"We don't know each other, we have only spoken on the phone," Putin said at an investment forum in Moscow.

The Russian president added however that although he has "no relationship" with his Ukrainian counterpart, a former comedian inaugurated in May, he believes "Zelensky is a likeable man and sincere."

"I think he really wants to change the situation for the better, including in the Donbas," he said, referring to the area of eastern Ukraine run by Russia-backed separatists.

"To what extent he is able to carry this out, I don't know yet," Putin said.

"Some positive steps have been taken," he added, naming the pull-back of troops and equipment along a portion of the line of contact between Ukrainian forces and the separatists.

The pull-back completed early this month was a precondition for a face-to-face meeting during a summit mediated by leaders of France and Germany aiming to end the five-year conflict.

The summit, scheduled in Paris on December 9, will be the highest-level negotiation on the conflict since 2016.

Recent moves to ease tensions have included an exchange of prisoners in September and Moscow's return this week of three Ukrainian ships seized last year.

Although Zelensky was elected on a promise to end the conflict in eastern Ukraine, he is also facing strong criticism at home from those who see him as caving into demands from Moscow.

Critics warn that Zelensky may make too many concessions at the summit at the expense of Ukrainian sovereignty, particularly on issues such as elections in the separatist areas and the control of the long border with Russia.

Ukraine's foreign minister on Tuesday said Kyiv is "expecting to reach real progress" in Paris.

Foreign Minister Vadym Prystaiko said Ukraine would go to the talks "with open ideas, an open mind.

"We are ready for a reasonable compromise and to take home progress which the Ukrainians are eagerly awaiting.