Ukraine on Sunday slammed Pope Francis's call to negotiate with Russia two years into its invasion, vowing "never" to surrender after the pontiff said Kyiv should "have the courage to raise the white flag".

The Catholic leader had fuelled anger in Kyiv after saying in an interview published Saturday that Ukraine should negotiate with Russia, which has seized large swathes of its territory during the war.

"Our flag is a yellow and blue one. This is the flag by which we live, die, and prevail. We shall never raise any other flags," Ukraine's Foreign Minister Dmytro Kuleba said on social media.

While battling its bigger neighbour, Ukraine has vowed not to give up its territory.

The Pope fuelled anger by saying: "When you see that you are defeated, that things are not working out, to have the courage to negotiate."

Kuleba called on the elderly pontiff to stand "on the side of good" and not put the opposing sides "on the same footing and call it 'negotiations'."

He also appeared to reference some of the Catholic church collaborating with Nazi forces during World War II:

"At the same time, when it comes to the white flag, we know this Vatican strategy from the first half of the 20th century," Kuleba said.

"I urge to avoid repeating the mistakes of the past and to support Ukraine and its people in their just struggle for their lives."

He also thanked Pope Francis for his "constant prayers for peace" and said Kyiv hoped the cleric would visit Ukraine.

"We continue to hope that after two years of devastating war in the heart of Europe, the Pontiff will find an opportunity to pay an Apostolic visit to Ukraine to support over a million Ukrainian Catholics, over five million Greek-Catholics and all Ukrainians," Kuleba said.

© Agence France-Presse