The war in Ukraine has sparked a war of sorts between Christian churches. According to the Vatican, Pope Francis scolded Patriarch Kirill, the head of the Russian Orthodox Church, in a phone conversation in early March.

"We are shepherds of the same holy people who believe in God, in the Holy Trinity, in the holy mother of God. That is why we must unite in the effort to help peace, to help those who suffer, to seek ways of peace, to stop the gunfire," the Pope told the patriarch, according to Vatican sources.

The Pope added that "those who pay the bill for the war are the people; it is both the Russian soldiers and the people who are being bombed and die."

"There was a time when we spoke, even in our churches, of a holy war or a just war. Today we cannot speak like that. The Christian conscience of the importance of peace has developed," the Pope said.

The Vatican spokesman said Pope Francis and Patriarch Kirill agreed that the Catholic and Orthodox Churches are called "to contribute to strengthening peace and justice." The two also agreed that "the church must not use the language of politics but the language of Jesus," the Vatican said.

Eastern Orthodox churches like the Russian Church are not under the Pope's jurisdiction, and are not centralized like the Roman Catholic Church. Each autonomous national church makes its own policies under independent leadership.

The Pope does have a direct interest in the Ukraine, because about 11% of the Ukrainian population is Catholic. The rest are Orthodox – most of them adhering to the Ukrainian Orthodox Church – but some in the country's Russian-speaking eastern regions following Kirill's Russian Orthodox Church.

Kirill has also been feuding with another powerful Orthodox patriarch – the Istanbul-based Benjamin of Constantinople – over the status of the Ukrainian churches. Benjamin has recognized the Ukrainian Church's independence from Moscow, while Kirill insists that he has jurisdiction over Ukraine.

Benjamin has also been critical of Russia's invasion of Ukraine, which Kirill has blessed.

Other Christian leaders have jumped into the fray. Ioan Sauca, general secretary of the World Council of Churches, has also condemned the war and appealed to Kirill to use his influence with Russian President Vladimir Putin to bring it to an end.

In a letter, Kirill responded by repeating Putin's claim that Russians and Ukrainians share a common national history, going back to what is known as "Kievan Rus" in the ninth century CE.

"As you know, this conflict did not start today," Kirill wrote.

"It is my firm belief that its initiators are not the peoples of Russia and Ukraine, who came from one Kievan baptismal font, are united by common faith, common saints, and prayers, and share common historical fate. The origins of the confrontation lie in the relationships between the West and Russia."

Some religious leaders are now going a step further, urging the World Council of Churches to expel the Russian Orthodox Church for acting contrary to the WCC mission of fostering Christian unity, peace, and justice.