KYIV, Ukraine — Air-raid sirens sounded temporarily in cities throughout Ukraine on Christmas morning after the authorities had warned for days that Russia’s military planned another wave of missile attacks.
The air-raid alert went into effect shortly after 9 a.m. on Sunday and covered all regions of Ukraine. Shortly after 11 a.m., the authorities canceled the alert for most regions, and there were no immediate reports of Russian strikes hitting their targets.
In Kyiv, some residents said they had heard explosions in the sky from air defense weapons.
Through the fall and start of winter, Russian forces have fired volleys of cruise missiles and launched drones at Ukrainian cities, aimed at energy and heating infrastructure. Military analysts have said it is part of a Russian strategy of plunging the country into darkness and cold to demoralize the population.
The bombardments have typically come at intervals of about a week. The actions on Sunday that touched off the air alert could have been either Russia firing missiles or sending planes into the air that set off false alarms.
But the air-raid alarms are disruptive even when sounded as a precaution — for example, when Russian planes are in the air — and no actual strikes follow the sirens.
During the alerts, Ukrainians often move to corridors, bathrooms or other areas in their homes — away from windows — that are deemed safer in case of a strike. Some people go to basements or quickly bundle their children into warm clothing to seek shelter in a subway station.
Ukraine celebrates Christmas as a national holiday on Dec. 25 — in line with the Western calendar — as well as on Jan. 7, for churches observing the Eastern Orthodox religious holiday.
Because of the war and electricity deficits from the Russian strikes on infrastructure, the Ukrainian capital is mostly devoid of holiday lights and decorations. But the authorities set up a Christmas tree on a central square that is illuminated with generator-powered lights, so it has continued to shine even during the frequent blackouts.
On Saturday, hours after Russian shelling ripped through the center of the southern city of Kherson, killing at least 10 people, President Volodymyr Zelensky of Ukraine said that the holidays “have a bitter aftertaste for us this year.”
“Dinner at the family table cannot be so tasty and warm. There may be empty chairs around it,” he said in a Christmas Eve message. “And our houses and streets can’t be so bright. And Christmas bells can ring not so loudly and inspiringly. Through air raid sirens, or even worse — gunshots and explosions.”
On Sunday, the Ukrainian military said that three demining experts had been killed in an explosion in the Kherson region a day earlier while clearing mines and unexploded ordnance after the Russian military’s retreat from the area last month.
Towns closer to the front line were hit by artillery overnight, Ukrainian officials said on Sunday. Russian artillery fired into the town of Nikopol in southern Ukraine, the head of the regional military administration, Valentyn Reznichenko, said.
Nikopol sits on the western bank of the Dnipro River, overlooking the Russian-occupied Zaporizhzhia Nuclear Power Plant on the opposite shore. Ukraine has accused the Russian military of firing artillery that is based on or near the plant’s grounds to strike Nikopol with impunity, as the Ukrainian military cannot return fire without risking hitting reactors or supporting safety equipment.
“The Russians do not stop mocking us in Nikopol,” Mr. Reznichenko said of the overnight strikes, according to Ukrainska Pravda, a Ukrainian news outlet.