STORY: The steel works has been rocked by heavy explosions as Russian forces fight for control of the last Ukrainian stronghold in the city.
Video released by the Azov Regiment on Thursday appeared to show heavy shelling.
The location of the video was verified by buildings which matched satellite imagery. On May 4, the regiment reported heavy shelling on the steel plant that continued on May 5.
The Azov Battalion was set up in 2014 as a group comprising pro-Ukrainian nationalist volunteers who fought against pro-Russian separatists in eastern Ukraine. Kyiv later incorporated the Azov fighters as a regiment in its National Guard. Russia accuses the group of being a neo-Nazi organisation, an allegation Ukraine rejects as pure propaganda.
An estimated 200 Ukrainian civilians including women and children remained trapped in the underground bunkers of the steel works with little food or water on Thursday, and the United Nations said a new operation was underway to evacuate more people.
Russian President Vladimir Putin said Russia was prepared to provide safe passage out for civilians, but reiterated calls for Ukrainian forces inside to disarm. Clinging on desperately, Ukrainian fighters have reported fierce battles with Russian troops.
Ukraine's stubborn defence of Azovstal has underlined Russia's failure to take major cities in a 10-week-old war that has united Western powers in arming Kyiv and punishing Moscow with sanctions.