CNN  — 

Russian President Vladimir Putin declared a brief Easter ceasefire in his war with Ukraine, a declaration met with skepticism in Kyiv as the grinding war enters a crucial phase.

Putin said “all hostilities” will halt between 6 p.m. Moscow time on Saturday (11 a.m. ET) and midnight on Monday (5 p.m. Sunday ET).

“We assume that the Ukrainian side will follow our example,” he added.

The announcement came just hours after Russia’s Defense Ministry announced its forces pushed Ukrainian troops from one of their last remaining footholds in Russia’s Kursk region where the Ukrainians staged a surprise incursion last year.

Putin said the truce will help Russia determine how sincere Kyiv is about wanting to reach a ceasefire.

Kyiv reacted with skepticism. Ukrainian President Volodymyr Zelensky posted to X shortly after the Russian leader announced the truce, calling the announcement “yet another attempt by Putin to play with human lives.”

Air raid sirens sounded in Kyiv soon after Putin’s announcement, with the city’s military administration warning of a Russian drone. Officials urged people not to leave shelters until the alert was over. Sirens sounded in several other Ukrainian regions.

“At this moment, air raid alerts are spreading across Ukraine,” Zelensky said. “Shahed drones in our skies reveal Putin’s true attitude toward Easter and toward human life,” he added.

The Ukrainian leader’s post did not make it immediately clear whether or not Kyiv will accept the truce. If it does accept, this will be the first pause in the conflict since Russia’s February 2022 full-scale invasion. CNN has approached the Ukrainian presidency for comment.

Ukraine has previously been skeptical about such temporary pauses in conflict, having rejected a temporary ceasefire in January 2023 believing that Russia had ulterior motives in calling for a stop to the fighting, such as using the pause to bring in more troops.

Like on Saturday, the 2023 truce was announced by Putin to coincide with a holiday – this time with Orthodox Easter, back then with Orthodox Christmas.

The announcement comes at a pivotal time for the war.

As well as in Kursk, fighting continues along the eastern frontline, which has barely moved in the past three years as neither side has been able to make significant gains.

While Ukraine has recently managed to push Russian troops back from areas around Toretsk, Russia has been inching forward near Kupyansk, Lyman and Kurakhove, according to the Institute for the Study of War, a US-based conflict monitor.

Separately, the two sides conducted one of the largest prisoner exchanges of the conflict on Saturday.

According to Zelensky, 277 captured Ukrainian soldiers were returned home. The Russian Defense Ministry said it swapped 246 captured Ukrainian soldiers swapped for the same number of Russian troops, and that as a “gesture of good will” Russia also exchanged 31 wounded Ukrainian troops for 15 wounded Russian servicemen.

At the same time, US-led peace efforts are stuttering, as Moscow continues to stall having previously rejected a US proposal for a 30-day ceasefire.

On Friday, US Secretary of State Marco Rubio warned that the US was ready to “move on” from efforts to bring peace to Ukraine within days if there were no tangible signs of progress.

This is a developing story and will be updated.