KYIV, Ukraine — An uneasy calm in Kyiv on Friday was broken by air-raid sirens that also blared across the rest of Ukraine as a Russian cease-fire declaration for the Orthodox Christmas took effect. Ukrainian and Western officials have scorned the truce as a ploy.

No explosions were heard in the capital. And reports of sporadic fighting elsewhere in Ukraine could not immediately by confirmed. Clashes there could take hours to become public.

Kyiv residents ventured out into a light dusting of snow to buy gifts, cakes and groceries for Christmas Eve family celebrations, hours after the cease-fire was to have started.

Russian President Vladimir Putin on Thursday ordered his forces in Ukraine to observe a unilateral, 36-hour cease-fire. Kyiv officials dismissed the move but didn’t clarify whether Ukrainian troops would follow suit.

Moscow also didn’t say whether its forces would retaliate if Ukraine kept fighting, but the Moscow-appointed head of the Donetsk region, Denis Pushilin, said they would.

The Russian-declared truce in the nearly 11-month war began at noon Friday and was to continue through midnight Saturday Moscow time (0900 GMT Friday to 2100 GMT Saturday; 4 a.m. EST Friday to 4 p.m. EST Saturday).

Air-raid sirens sounded in Kyiv about 40 minutes after the Russian cease-fire was to come into effect. The widely used “Alerts in Ukraine” app, which includes information from emergency services, showed sirens blaring across the country.

Russia's Defense Ministry alleged that Ukrainian forces continued to shell its positions, and said its forces returned fire to suppress the attacks. But it wasn’t clear from the statement whether the attacks and return of fire took place before or after the cease-fire took effect.

The ministry's spokesman, Igor Konashenkov, reported multiple Ukrainian attacks in the eastern Donetsk, Luhansk and Zaporizhzhia regions. It was not possible to verify the claims.

Putin’s announcement Thursday that the Kremlin’s troops would stop fighting along the more than 1,000-kilometer (680-mile) front line and elsewhere was unexpected. It came after the head of the Russian Orthodox Church, Patriarch Kirill, proposed a cease-fire for the Christmas holiday. The Orthodox Church, which uses the Julian calendar, celebrates Christmas on Jan. 7.

But Ukrainian and Western officials 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.

“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,” Ukrainian President Volodymyr Zelenskyy said late Thursday.

He didn't, however, state outright that Kyiv would ignore Putin’s request.

In a Christmas Eve message to the nation, Zelenskyy called it "a holiday of harmony and family unity. And together we are all a big Ukrainian family.

“No matter where we are now — at home, at work, in a trench, on the road, in Ukraine or abroad — our family is united as never before. ... United in its belief in a single victory.”

U.S. President Joe Biden has also expressed wariness about the Russian cease-fire, saying it was “interesting” that Putin was ready to bomb hospitals, nurseries and churches in recent weeks on Christmas and New Year’s.

“I think (Putin) is trying to find some oxygen,” Biden said.

U.S. State Department spokesman Ned Price said Washington had “little faith in the intentions behind this announcement,” adding that Kremlin officials ”have given us no reason to take anything that they offer at face value.”

The Institute for the Study of War agreed the truce could be a ruse allowing Russia to regroup.

“Such a pause would disproportionately benefit Russian troops and begin to deprive Ukraine of the initiative,” the think tank said late Thursday. "Putin cannot reasonably expect Ukraine to meet the terms of this suddenly declared cease-fire, and may have called for the cease-fire to frame Ukraine as unaccommodating and unwilling to take the necessary steps toward negotiations.”

And Anna Borshchevskaya, a senior fellow at the Washington Institute, said that whether or not the cease-fire holds, “I don’t take it at face value.”

“When Russia announces cease-fires, in the way Russia conducts war, there are usually ulterior motives,” she said. “Historically, what the Russian government and Russian military usually do when they announce a cease-fire is to use it as a tactical opportunity, to just take a breather or gain a little bit of space.”

Meanwhile, the U.S. was due to reinforce its support for Ukraine on Friday by announcing nearly $3 billion in military aid — a major new package expected for the first time to include several dozen Bradley fighting vehicles.

Germany also plans to send armored personnel carriers by the end of March.

On the streets of Kyiv, some civilians said Friday that they spoke from bitter experience in doubting Russia’s motives.

“Everybody is preparing (for an attack), because everybody remembers what happened on the new year when there were around 40 Shahed" Iranian drones, said capital resident Vasyl Kuzmenko. “But everything is possible.”

At the Vatican, Pope Francis said he was sending wishes from his heart “to the Eastern churches, both the Catholic and the Orthodox ones, that tomorrow will celebrate the birth of the Lord.” Speaking to thousands of faithful gathered in St. Peter’s Square for the Epiphany feast day, Francis said, “In a special way, I would like my wish to reach the brothers and sisters of martyred Ukraine," and prayed for peace there.