Ukraine on Monday summoned the Vatican's envoy to Kiev after Pope Francis suggested the country should consider raising "the white flag" amid the ongoing war with Russia.

Ukraine has angrily rejected Pope Francis' suggestion to negotiate with Russia two years after the start of the war, vowing "never" to surrender.

"Due to the statements of Pope Francis the Apostolic Nuncio was invited to the ministry of foreign affairs of Ukraine," the ministry said on social media, using the term for a Vatican diplomat.

It added that the envoy, Visvaldas Kulbodas, was told Kiev was "disappointed with the words of the Pontiff regarding the 'white flag'."

The ministry said the Catholic leader's words "encourage them (Russia) to further disregard international law."

"The head of the Holy See should have sent signals to the international community about the need to immediately unite forces to ensure the victory of good over evil, as well as appealed to the attacker, not the victim," it added.

The 87-year-old pontiff had said in an interview with Swiss broadcaster RTS conducted in early February and broadcast on Saturday, "I believe that the strongest are those who see the situation, think about the people and have the courage to raise the white flag and negotiate."

"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.