Ukraine's shelling killed and wounded its own civilians in the southern region of Kherson, Russia said on Sunday, while some civilians managed to leave a steel plant in besieged Mariupol.

U.S. House of Representatives Speaker Nancy Pelosi, meanwhile, became the latest Western official to visit Kyiv in a show of support for Ukraine.

"We believe that we are visiting you to say thank you for your fight for freedom. ... Your fight is a fight for everyone. Our commitment is to be there for you until the fight is done," Pelosi said in a video shared by President Volodymyr Zelenskyy on Twitter.