The head of the Russian Orthodox Church has told Russian soldiers that death in Ukraine will absolve them of all sins.
Patriarch Kirill, who in February justified Putin's decision to invade Ukraine on spiritual and ideological grounds, made the remarks after Moscow said up to 300,000 reservists would be called up to fight.
The decision has sparked pockets of protests across Russia, with one monitoring group reporting more than 700 people being detained in 32 different cities.
Russia's top priest said: "Willingness to make sacrifices is the greatest expression of the best of human qualities.
"We know that today many die in the fields of internecine warfare. The Church prays that this battle will end as soon as possible, that as few brothers as possible will kill each other in this fratricidal war."
He then went on to reassure those called up to fight that should they die, their death would be a "sacrifice" and would "cleanse" their sins.
He said: "At the same time, the Church realises that if someone, guided by a sense of duty, by the need to be loyal to the oath, remains true to his calling and goes to fulfil what their duty calls, and if that person dies while fulfilling this duty, he is undoubtedly accomplishes an act that equals a sacrifice.
"He sacrifices himself for the others.
"That is why we believe that this sacrifice cleanses all the sins that a person has committed."
Patriarch Kirill also said in his sermon on Sunday that he prayed for the fighting to end.
Last week Russia began its first military mobilisation since World War Two to enlist citizens to fight in Ukraine.
Vladimir Putin announced plans to mobilise 300,000 reserves to fight in the war in Ukraine, prioritising those with combat experience. He signed a new decree on Saturday that soldiers who surrender, desert, or refuse to fight can face up to 10 years in prison.
Watch: Putin mobilises 300,000 more troops for Ukraine
Last week, after the mobilisation announcement, Kirrill said in a sermon that a person of "true faith" is not subject to the fear of death.
He said that a person becomes "invincible" when there is a "strong dimension associated with eternity" in him, and he ceases to be afraid of death.
"Faith makes a person very strong, because it transfers his consciousness from everyday life, from material worries, to caring for the soul, for eternity," he said. "Namely, the fear of death drives a warrior from the battlefield, pushes the weak to betrayal and even to rebel against their brothers. But true faith destroys the fear of death."
On Monday a report by independent Russian media outlet Meduza, which is based in Latvia, suggested that men of military age could be banned from leaving the country, as thousands try to flee Putin's call-up.
The initial call to action led thousands to try and escape the country, with tickets to neighbouring countries Turkey and Azerbaijan - neither of which require visas for Russians - selling out within hours and thousands traveling to Finland by land.
The ban is expected to be introduced on Wednesday, after voting in the referendums in Russian-seized areas of Luhansk, Donetsk, Kherson, and Zaporizhzhia in Ukraine has ended.
British Foreign Secretary James Cleverly told the Mirror: “We know what Vladimir Putin is doing.
“He is planning to fabricate the outcome of those referenda, he is planning to use that to annex sovereign Ukrainian territory, and he is planning to use it as a further pretext to escalate his aggression.”