Mariupol has been besieged by Russian troops and pro-Russia separatists for more than a month and has seen some of the fiercest urban warfare in the conflict in Ukraine. Fighting has leveled much of the city, and the civilian death toll so far isn’t known. Many residents have been unable to evacuate, trapped without power or essential supplies.

An analysis of satellite images by Masae Analytics, a company that uses photography to assess building damage, found that much of the city had been hit as of April 5.

Mariupol is a strategic objective for Moscow. Taking the city would create an overland corridor from Russia across the northern lip of the Azov Sea to the Russia-annexed Crimean Peninsula. Here is a closer look at some of the hardest-hit regions.

City Center

Around 400,000 people lived in Mariupol before the war. Near the city center, a Russian airstrike March 9 hit a maternity hospital, killing three people and wounding 17, the mayor said. A wide, deep crater was visible, with signs that the blast, which took place around 5 p.m. local time, had knocked down trees and torched cars.

A week later, at least 300 people were killed in a theater bombed by Russian forces, local authorities said. About 1,000 civilians had been sheltering there. Days later, an art school in the district that was sheltering about 400 Mariupol residents, including women and children, also was attacked.

A street in central Mariupol, as seen from the damaged theater on April 12.

Photo: ALEXANDER NEMENOV/Getty Images

People walk past a crater from an explosion in March.

Photo: Evgeniy Maloletka/Associated Press

A woman stands outside a destroyed maternity hospital where three were killed on March 9.

Photo: Evgeniy Maloletka/Associated Press

Inside Mariupol’s theater in early April.

Photo: Alexei Alexandrov/Associated Press

Industry

A focal point of fighting has been the areas around two massive steel plants, Azovstal and Illich Iron and Steel Works, that used to employ about 40,000 people in the city.

Azovstal to the east of the Kalmius River and Illich to the north of the city, dominate Mariupol and are an industrial prize for invading forces. Before Russia instituted a naval blockade last month, Mariupol’s port handled these steel exports along with other products, largely grain and clay.

Another Ukrainian steel company, Metinvest, said last Tuesday that production at its site in Mariupol would likely be delayed after “reportedly sustained further damage from hostilities.”

Damaged homes near the Azovstal Iron and Steel Works on March 28.

Photo: Alexander Ermochenko/Reuters

A satellite image provided by Maxar Technologies shows damage at the Azovstal factory in March.

Photo: Maxar Technologies/Shutterstock

A man walks near the Illich Steel and Iron Works in April.

Photo: Alexander Ermochenko/REUTERS

Residential Areas

No part of Mariupol has been more cut off than the left bank, which includes the Livoberezhnyi district. The area east of the Kalmius River has been pulverized by Russian shelling and left without phone and internet access.

On the western edge of the city, intense shelling destroyed many apartment buildings.

The International Committee of the Red Cross has tried to reach the city to evacuate the 160,000 people believed to be trapped there, but a civilian-evacuation team said on April 1 “conditions made it impossible to proceed.”

A satellite image shows destroyed residential buildings in eastern Mariupol’s Livoberezhnyi district.

Photo: MAXAR TECHNOLOGIES/GETTY IMAGES

A drone photo of damaged apartments on April 3.

Photo: PAVEL KLIMOV/REUTERS

Ukrainians walk along a street in western Mariupol.

Photo: Sergei Bobylev/Zuma Press

—Kara Dapena and Brian McGill contributed to this article.

Write to Taylor Umlauf at Taylor.Umlauf@wsj.com