Ukrainian President Volodymyr Zelenskyy has said he would only agree to see Russian President Vladimir Putin after a plan on Ukraine is negotiated with US President Trump.

Speaking at the Munich Security Conference on Friday, Zelenskyy said that he was open to negotiations but expected any potential peace talks with Russia to be extremely difficult.

The Ukrainian president described acknowledging the Russian annexation of Ukrainian territory as a "red line" that would never be recognized.

He believes that Trump was the key to ending the conflict in his country, telling reporters at the MSC that the US leader had given him his personal phone number during a call earlier this week.

"Yes, he gave me his telephone number," Zelenskyy said, adding that Trump had told the Ukrainian leader: "You can call anytime."