KYIV, Ukraine (AP) — The impact of Russian President Vladimir Putin’s order for his forces in Ukraine to observe a unilateral, 36-hour cease-fire was in doubt Friday after Kyiv officials dismissed the move as a ploy but didn’t clarify whether Ukrainian troops would follow suit.

Moscow also didn’t say whether it would hit back if Ukraine kept fighting.

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 am EST Friday to 4 pm EST Saturday). There were no immediate reports of it being broken.

Air raid sirens sounded in Kyiv about 40 minutes after the Russian cease-fire was to come into effect, but no explosions were heard. A widely-used Alerts in Ukraine app, which includes information from emergency services, showed sirens blaring all across the country.

Putin’s announcement Thursday that the Kremlin’s troops would stop fighting along the 1,100-kilometer (684-mile) front line or 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.

Ukrainian President Volodymyr Zelenskyy questioned the Kremlin’s intentions, accusing the Kremlin of planning the fighting pause “to continue the war with renewed vigor.”

“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,” Zelenskyy said late Thursday.

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

US President Joe Biden echoed Zelenskyy’s wariness, saying it was “interesting” that Putin was ready to bomb hospitals, nurseries and churches on Christmas and New Year’s.

“I think (Putin) is trying to find some oxygen,” Biden said, without elaborating.

US 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 truce order seems to be a ploy “to rest, refit, regroup, and ultimately reattack,” he said.

The Institute for the Study of War agreed that 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.”

Washington says it’s prepared to keep backing Ukraine’s war effort. On Friday, the US was due to announce nearly $3 billion in military aid for Ukraine — a major new package that was expected for the first time to include several dozen Bradley fighting vehicles.

The ill-feeling between the warring sides showed no signs of abating, despite the backdrop of Christmas.

Former Russian President Dmitry Medvedev, the deputy head of Russia’s Security Council, said those who rejected Putin’s proposal for a Christmas truce were “clowns” and “pigs.”

“The hand of Christian mercy was extended to the Ukrainians,” he said in a Telegram post. “But pigs have no faith and no innate sense of gratitude.”

Some civilians on the streets of Kyiv said 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),” local resident Vasyl Kuzmenko said. “But everything is possible.”