Russian forces tightened the noose around the defenders holed up Wednesday in a mammoth steel plant that represented the last known Ukrainian stronghold in Mariupol, as a fighter apparently on the inside pleaded on a video for help: “We may have only a few days or hours left.” On the battlefield, Ukraine said Moscow continued to mount assaults across the east, probing for weak points in Ukrainian defensive lines. Russia said it launched hundreds of missile and air attacks on targets that included concentrations of troops and vehicles. Watch the video for more.