Ukraine's capital Kyiv marked Orthodox Christmas in the shadow of war on Saturday with a service under tight security at the city's 1,000-year-old monastery.
It came as Russian President Vladimir Putin saluted the Russian Orthodox Church for backing the military campaign in Ukraine.
There were reports of artillery fire being exchanged. Russia purportedly observed a 36-hour ceasefire. The Ukrainian side was suspicious of the suggestion and each party blamed the other for the shelling.
The Orthodox Church is the dominant religious group in both countries and celebrates Christmas according to the Julian calendar.
Metropolitan Epifaniy, the head of Ukraine's church, led a service on Saturday in Kyiv's Pechersk Lavra monastery, a Unesco world heritage site.
The passports of hundreds of worshippers were checked and people were scanned by metal detectors under a tight police presence, AFP reported.
Ukrainian churches that were once under the jurisdiction of Moscow's patriarch have formally severed ties, although authorities in Kyiv are suspicious. The security service raided the monastery in November and claimed it had found pro-Russian literature there.
Moscow's Patriarch Kirill, the senior cleric in Russia and a Russian loyalist, has been sanctioned in the West for supporting the invasion of Ukraine.
In a message published by the Kremlin, Mr Putin thanked the Russian church for “supporting our warriors taking part in the special military operation”.
Photos showed him attending a midnight service alone at the Cathedral of the Annunciation within the walls of the Kremlin.
“It is deeply gratifying to note the enormous constructive contribution of the Russian Orthodox Church and other Christian denominations in unifying society, preserving our historical memory, educating youth and strengthening the institution of family,” Mr Putin said.
The 36-hour ceasefire announced by Mr Putin on Thursday was rejected by Ukraine and its allies, who said Russia could use it to regroup its forces.
The US said fighting continued into the ceasefire window, and exchanges of artillery fire were reported on Saturday.
Moscow's Defence Ministry claimed it was returning Ukrainian fire and insisted it would maintain a ceasefire until Midnight.
In his Christmas message, Ukrainian President Volodymyr Zelenskyy said the country was “united as never before” in resisting Russia.
He spoke of a spirit of hope brought about by Ukraine's “courage, indomitability and invincibility” since Russia invaded on February 24.
Kyiv and other cities have been under a barrage of Russian missile and drone attacks in recent weeks, leaving many people without power in winter.
“Today we all have one dream. May harmony come to every family, welfare to every home, victory to the Ukrainian land,” Mr Zelenskyy said.
