KYIV, Ukraine (AP) — More than 20 people have been killed in a Russian missile strike on the Ukrainian city of Sumy, the city’s acting mayor said Sunday.

Two ballistic missiles struck the heart of the city as local people gathered to celebrate Palm Sunday.

“On this bright Palm Sunday, our community has suffered a terrible tragedy,” Artem Kobzar said in a statement on social media. “Unfortunately, we already know of more than 20 deaths.”

The strike comes less than a day after Russia and Ukraine’s top diplomats accused each other of violating a tentative U.S.-brokered deal to pause strikes on energy infrastructure, underscoring the challenges of negotiating an end to the 3-year-old war.