ROME – In some of his strongest language yet on the Ukraine war, Pope Francis Thursday told a delegation of Orthodox leaders that the conflict in Ukraine amounted to a “war of aggression” that was unacceptable for Christians to support.

Speaking to a delegation from the Ecumenical Patriarchate of Constantinople who were in Rome to celebrate the Catholic Feast of Saints Peter and Paul, Francis in his June 30 speech stressed the importance of Christian unity at a time when “our world is disrupted by a cruel and senseless war of aggression in which many, many Christians are fighting one another.”

Although he did not specifically name the aggressor in the conflict, he lamented the suffering of those “who have lost their loved ones and been forced to abandon their homes and their own country!”

In an apparent response to Russian Orthodox Patriarch Kirill’s defense of the Ukraine war as a defense of Christian values, Francis stressed the need for conversion, saying there is a need to recognize that “armed conquest, expansionism and imperialism have nothing to do with the Kingdom that Jesus proclaimed.”

This attitude, he said, has “nothing to do with the risen Lord, who in Gethsemane told his disciples to reject violence, to put the sword back in its place, since those who live by the sword will die by the sword.”

Pope Francis insisted that the quest for Christian unity should prompt all Christians to ask themselves what kind of world they want to see in the wake of “this terrible outbreak of hostilities and conflict,” and what contribution they are prepared to make towards achieving a more “fraternal humanity.”

Answers to these questions, he said, come from the Gospel, where Jesus “calls us to be merciful and never violent, to be perfect as the Father is perfect, and not be conformed to the world.”

He urged Christians not to “yield to the temptation to muffle the explosive newness of the Gospel with the seductions of this world,” and cautioned against turning God “into the god of our own ideas and our own nations.”

“Let us start anew from him, and recognize that it is no longer the time to order our ecclesial agendas in accordance with the world’s standards of power and expediency, but in accordance with the Gospel’s bold prophetic message of peace,” he said.

Though he did not specifically name Ukraine or Russia or identify who he believed was responsible for the war, Francis’s description of the conflict as an act of “aggression” and his condemnation of expansionist ideals at odds with the Gospel of Christ appear to be one of his most direct rebukes of Russian President Vladimir Putin and Kirill over their justification of the war.

These remarks from Pope Francis come as he faces increased criticism over some of his public comments on the Ukraine war suggesting that there are no clear “good guys” or “bad guys” in the conflict, and that Russia was perhaps antagonized into its Feb. 24 invasion of Ukraine by NATO forces “barking” at its door.

Controversy over the pope’s remarks has escalated to the point that the Latin rite Bishop of Kyiv, Vitaliy Krivitskiy, said in a recent interview that he no longer believes a papal visit to Ukraine is possible, because he is no longer seen as “non-partisan.”

Speaking to Avvenire, the official newspaper of the Italian bishops, Krivitskiy said “compared to the beginning of the conflict, a part of the population did not welcome the pope’s words, which were considered incorrect.”

For the pope to visit Ukraine, it is necessary “to reconstruct a ‘consensus’ around his journey,” Krivitskiy said, noting that “some here no longer consider him super partes (nonpartisan).”

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In a conversation with editors of the Jesuit-run paper La Civiltà Cattolica that was published earlier this month, Francis, referring to the war in Ukraine, said, “There are no metaphysical good guys and bad guys here, in an abstract way.”

He suggested that the war was a result of several “intertwined” factors and recalled a conversation with an unidentified head of state prior to Russia’s invasion of Ukraine in which the politician apparently said NATO was “barking at Russia’s doorstep.”

Pope Francis also condemned the global arms trade and has refrained from voicing outright support for arming Ukraine in its fight against Russia.

Despite the pope’s many appeals for peace and public gestures such as kissing a Ukrainian flag from Bucha, where alleged war crimes occurred, he has yet to name Russia or Russian President Vladimir Putin as aggressors in the conflict, leaving many Ukrainians confused as to where he actually stands.

The pope’s remarks have even drawn criticism from close allies, including his longtime friend from Buenos Aires, Major Archbishop Sviatoslav Shevchuk, who oversees the Greek Catholic Church in Ukraine and who has advocated for a papal visit to Ukraine for years.

In an apparent response to the pope’s remarks in La Civiltà Cattolica, Shevchuk in a recent video message said, “the causes of this war lie within Russia itself. And the Russian aggressor is trying to solve its internal problems with the help of external aggression.”

“Russia’s aggression against Ukraine is completely unprovoked,” he said. “Anyone who thinks that some external cause has provoked Russia into military aggression is either themselves in the grip of Russian propaganda or is simply and deliberately deceiving the world.”

Pope Francis also recently granted a nearly two-hour audience with a small group of Ukrainians who were concerned about his “ambiguous” rhetoric on the war.

RELATED: Ukrainians meet pope to bridge ‘ambiguous’ communication gap

It is unclear if the pope’s remarks Thursday signal a more sweeping change in tone in terms of his position on the war, or if he was using stronger language given his audience, as the Patriarchate of Constantinople has traditionally been at odds with the Patriarchate of Moscow over its openness to the West.

Follow Elise Ann Allen on Twitter: @eliseannallen