No explosions were heard in the Ukrainian capital, but any fighting elsewhere in the country could take hours to become public.
With uncertainty over whether the truce was holding, hours after it was due to have started at midday Moscow time on Friday (9am GMT), Kyiv residents ventured out to buy gifts, cakes and groceries for their Christmas Eve family celebrations.
Russian President Vladimir Putin ordered the 36-hour ceasefire in the nearly 11-month-long war in a surprise move on Thursday, saying it would mark the Russian Orthodox Christian Christmas.
The temporary truce was due to come into effect on Friday but the hours leading up to it saw renewed fighting, while Kyiv officials rejected the cease-fire as a ploy, and did not clarify whether Ukrainian troops would follow suit.
Moscow also didn’t say whether it would retaliate if Ukraine kept fighting, but the Moscow-appointed head of the Donetsk region, Denis Pushilin, said they would.
The Russian-declared truce was to continue through midnight Saturday Moscow time (9pm GMT).
Air raid sirens sounded in Kyiv around 40 minutes after the Russian cease-fire was to come into effect, but no explosions were heard.
The widely used Alerts in Ukraine app, which includes information from emergency services, showed sirens blaring all across the country.
The Russian military alleged that Ukrainian forces continued to shell its positions despite the truce that Kyiv never agreed to.
Russia’s Defence Ministry said its forces returned fire to suppress the attacks, although it wasn’t entirely clear from the statement whether the attacks and the return of fire took place before or after the cease-fire took effect.
Russian Defence Ministry spokesman Igor Konashenkov reported multiple attacks in the eastern Donetsk, Luhansk and Zaporizhzhia regions.
It was not possible to verify the claims.
Mr Putin’s announcement on Thursday that the Kremlin’s troops would stop fighting along the more than 680-mile front line and elsewhere was unexpected.
It came after the Russian Orthodox Church head, Patriarch Kirill, proposed a cease-fire for this weekend’s Orthodox Christmas holiday.
The Orthodox Church, which uses the Julian calendar, celebrates Christmas on January 7.
But Ukrainian and Western officials suspected an ulterior motive in Putin’s apparent goodwill gesture.
They portrayed the announcement as an attempt by Putin to grab the moral high ground while possibly seeking to snatch the battlefield initiative and rob the Ukrainians of momentum amid their counteroffensive of recent months.
Ukrainian President Volodymyr Zelensky questioned the Kremlin’s intentions, accusing the Kremlin of planning the fighting pause “to continue the war with renewed vigour.”
“Now they want to use Christmas as a cover to stop the advance of our guys in the (eastern) Donbas (region) for a while and bring equipment, ammunition and mobilized people closer to our positions,” Mr Zelensky said late on Thursday.
He didn’t, however, state outright that Kyiv would ignore Putin’s request.
British Foreign Secretary James Cleverly said it will “do nothing to advance the prospects for peace”.
He added: “Russia must permanently withdraw its forces, relinquish its illegal control of Ukrainian territory and end its barbaric attacks against innocent civilians.”