Mariupol unfortunately was always going to suffer the most. I grew up in Mariupol and still have family there so know it well.
The Russians are concentrating on Mariupol because it is geographically and strategically important, but also because from 2014 it became home to an extremist Neo-Nazi Battalion Azov, which started off as volunteers, but later became a very influential part of the Ukrainian National Guard.
The fear the locals have for them is unimaginable. They have links to terrorist organisations around the world, are influential, armed and kill willingly.
Since 2014 they have been reported for extreme violence, including rape, torture, executions etc. The first article links to the Report on the human rights situation in Ukraine in 2015 - 2016. It's 53 pages on violations of Human rights of Ukrainian Citizens.
I quote:
"In addition, Ukrainian armed forces continue to position themselves near towns and villages while armed groups have embedded deeper into residential areas, further endangering the local population. The risk of re-escalation of hostilities therefore remained high."
The same tactics are being used today. Ukrainian army position themselves in residential buildings, schools and hospitals.
www.aljazeera.com/news/2022/3/1/who-are-the-azov-regiment
time.com/5926750/azov-far-right-movement-facebook/
Human rights violations and war crimes
A 2016 report by the United Nations Office of the High Commissioner for Human Rights (OCHA) has accused the Azov regiment of violating international humanitarian law.
The report detailed incidents over a period from November 2015-February 2016 where Azov had embedded their weapons and forces in used civilian buildings, and displaced residents after looting civilian properties. The report also accused the battalion of raping and torturing detainees in the Donbas region.