The president of Poland’s Catholic bishops’ conference has urged the head of the Russian Orthodox Church to ask President Vladimir Putin to stop the war in Ukraine.

In a strongly worded letter dated March 2, Archbishop Stanisław Gądecki told Patriarch Kirill of Moscow that Putin could “stop the suffering of thousands of people with one word.”

“I ask you, Brother, to appeal to Vladimir Putin to stop the senseless warfare against the Ukrainian people, in which innocent people are being killed and suffering is affecting not only soldiers but civilians as well — especially women and children,” he wrote.

“One man can stop the suffering of thousands of people with one word — that man is the President of the Russian Federation. I ask you most humbly to call for the withdrawal of the Russian troops from the sovereign state that is Ukraine.”

The U.N. human rights office said on March 1 that it had recorded 536 civilian casualties since the Russian president ordered a full-scale invasion of Ukraine on Feb. 24. It said it had established that 136 civilians had been killed, including 13 children, and 400 injured, including 26 children, but that the real toll was likely to be higher.

The chief prosecutor of the International Criminal Court in the Hague, Netherlands, announced on March 2 that he was opening an investigation into alleged war crimes by Russia during its campaign.

The U.N. refugee agency reported on March 2 that more than 900,000 people had fled the fighting in Ukraine. More than half of them have found refuge in Poland, which shares a 332-mile border with the country.

Patriarch Kirill, who is believed to be close to Putin, has led the Russian Orthodox Church since 2009.

He commented on the war in Ukraine in an address at the Cathedral of Christ the Savior in Moscow on Feb. 27, saying: “May the Lord protect the peoples who are part of the united space of the Russian Orthodox Church from internecine strife.”

Ukraine is a predominantly Orthodox Christian country of 44 million people that borders Russia.

Eastern Orthodox Christians in Ukraine are divided between the Ukrainian Orthodox Church of the Moscow Patriarchate (UOC-MP), under the jurisdiction of the Russian Orthodox Church, and the Orthodox Church of Ukraine (OCU), which is affiliated with the Ecumenical Patriarchate of Constantinople.

In a speech on the eve of the invasion, Putin described Ukraine as an “inalienable part” of Russia’s “own history, culture and spiritual space.”

In his message to the patriarch, Gądecki referred to previous correspondence, thanking Kirill for “for the words conveyed in the letter of Metropolitan Hilarion,” the chairman of the Russian Orthodox Church’s Department of External Church Relations.

“I share the view of Your Holiness that hostility towards any nation is always unacceptable. We are all brothers, which is why we perceive every misfortune of the Ukrainian or Russian people as our own. Therefore, we wholeheartedly pray for peace in Ukraine,” the archbishop of Poznań, west-central Poland, wrote.

“However, so that our prayer may not be considered an expression of hypocrisy, it must be accompanied by actions. I believe, Your Holiness, that you are a man of peace. Our Lord, Jesus Christ taught: ‘Blessed are the peacemakers, for they shall be called sons of God’ (Matthew 5:9).”

Gądecki then called for the patriarch, the leader of more than 100 million Russian Orthodox Christians, to appeal directly to the Russian president to end the conflict.

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The archbishop went on: “No reason, no rationale can ever justify the decision to launch a military invasion of an independent country, bombing residential areas, schools, or kindergartens. War is always a defeat for humanity.”

“This war — as I wrote in the previous letter — is even more senseless because of the proximity of the two nations and their Christian roots. Is it permissible to destroy the cradle of Christianity on Slavic soil, the place where Rus was baptized?”

The archbishop was referring to the baptism of Prince Vladimir the Great, the ruler of Kievan Rus, in the year 988, an event that led to the Christianization of Russia.

He continued: “I also ask you to appeal to Russian soldiers not to take part in this unjust war, to refuse to carry out orders which, as we have already seen, lead to many war crimes. Refusing to follow orders in such a situation is a moral obligation.”

“The time will come to settle these crimes, including before the international courts. However, even if someone manages to avoid this human justice, there is a tribunal that cannot be avoided. ‘For we must all appear before the judgment seat of Christ, so that each one may receive good or evil, according to what he has done in the body’ (2 Corinthians 5:10).”

The Polish archbishop quoted a Russian soldier in Ukraine as saying: “We don’t know who to shoot at; they all look like us.”

“So, I ask you to appeal to them to go home as soon as possible without staining their hands with innocent blood,” Gądecki wrote.

The archbishop noted that Polish Catholics observed a day of prayer and fasting for peace in Ukraine on March 2, responding to an appeal by Pope Francis.

“I ask you, Brother, to call on all Orthodox brothers and sisters in Russia to engage in similar spiritual work,” he concluded. “I believe that the Lord God will not remain indifferent to our prayers and sacrifices. I believe that fasting and prayer change a person’s heart.”