Pope Francis on Sunday expressed great concern at the escalation in Ukraine after Moscow annexed four regions and Russian President Vladimir Putin threatened the use of nuclear weapons.

"My appeal is addressed first and foremost to the President of the Russian Federation, imploring him to stop this spiral of violence and death, also for the sake of his own people," Francis said to a crowd gathered at St. Peter’s Square in Vatican City.

"On the other hand, saddened at the immense suffering of the Ukrainian people as a result of the aggression they have suffered, I address an equally confident appeal to the President of Ukraine to be open to serious proposals for peace," he continued. "I urge all the protagonists of international life and the political leaders of nations to do everything possible to bring an end to the war, without allowing themselves to be drawn into dangerous escalations, and to promote and support initiatives for dialogue."

Russia on Friday annexed Ukraine’s Luhansk, Donetsk, Kherson and Zaporizhzhia regions after holding referendums there asking residents if they wanted to join Russia. The vote, which supposedly showed overwhelming support, was condemned by the West as a sham.

Ukraine over the weekend gained another military victory as they retook the strategic transportation hub of Lyman, a city located in one of the regions annexed by Russia. Get unlimited digital access Subscribe now for just $2 for 2 months.

Francis on Sunday also referenced Ukrainian cities like Bucha and Izyum, where Ukrainians have found mass graves after retaking the towns from Russian occupation, calling them "places of indescribable suffering and fear."

"This terrible and inconceivable wound to humanity, instead of healing, continues to shed even more blood, risking to spread further," the pope said. "I am saddened by the rivers of blood and tears spilled in these months."

Putin late last month also threatened the West with nuclear weapons as he faced steep territorial losses from a Ukrainian counteroffensive, claiming the threat is "not a bluff."

U.S. officials said they have seen no evidence yet that Russia is imminently moving to launch a nuclear weapon, but the threat led to consternation from Western officials and Ukraine as they warn of the grave consequences.

"And what about the fact that humanity is once again faced with the atomic threat?" Francis asked on Sunday.

"It is absurd," he added. "What is to happen next? How much blood must still flow for us to realize that war is never a solution, only destruction? In the name of God and in the name of the sense of humanity that dwells in every heart, I renew my call for an immediate ceasefire."

AE News