New Delhi, May 11 -- Russia and Ukraine swapped accusations of breaking a U.S.-brokered ceasefire on Sunday, with both sides claiming to have suffered casualties in drone and artillery strikes over the past 24 hours.

Ukraine's President Volodymyr Zelenskyy said that Russia was neither observing the truce nor "even particularly trying to," adding there had been no calm in front-line areas despite a lull in large-scale attacks and pledged that Ukraine would retaliate to any aggression shown by Moscow.

"Yesterday and today, Ukraine refrained from long-range retaliatory actions in response to the absence of large-scale Russian attacks," Zelenskyy said in evening statement, stressing Ukraine's increasing ability to hit targets far inside Rus...