By Pavel Polityuk and Natalia Zinets
(Reuters) - The port city of Mariupol on the Sea of Azov, reduced to a wasteland littered with bodies by nearly two months of siege and bombardment that Ukraine says killed tens of thousands of civilians, is a big strategic prize for Russia.
President Vladimir Putin on Thursday declared the city "liberated" after nearly two months of siege, despite leaving hundreds of defenders still holed up inside the giant Azovstal steel works.
Here is why the city matters so much:
Mariupol, home to more than 400,000 people before the war, is the biggest Ukrainian city on the Sea of Azov and the main port serving the industries and agriculture of eastern Ukraine. It is also the site of some of Ukraine's biggest metals plants.
On the eve of the war, it was the biggest city still held by Ukrainian authorities in Luhansk or Donetsk, the two eastern provinces known as the Donbas that Moscow has demanded Ukraine cede to pro-Russian separatists.
Control of Mariupol means Russia commands the entire coastline of the Sea of Azov, and has a secure overland route linking the Crimean peninsula, which Moscow seized and annexed in 2014, with mainland Russia and the parts of eastern Ukraine held by separatists.
It links up two of the main axes of Russia's invasion, and frees Russian forces to join the main offensive being waged against the bulk of Ukraine's army in the east.
Control of Mariupol could also give Russia a stronger position to negotiate at any peace talks.
Prominent among the Ukrainian forces that have defended Mariupol is the Azov Battalion, a nationalist militia started by far-right volunteers after Russian-backed separatists took control of parts of the eastern Donbas region in 2014.
Defence Minister Sergei Shoigu told Putin on Thursday that Mariupol had symbolic importance because it was what he called the de facto headquarters of the Azov Battalion.
Russia has said the destruction of that group is one of its main war aims as it tries to "denazify" Ukraine. Kyiv says the unit has been reformed and incorporated into the National Guard - and that Moscow is looking for a propaganda victory to cover over military setbacks elsewhere.
After days of ultimatums to surrender or die, Putin said on Thursday that the soldiers holding out in the steel plant would be treated with respect if they laid down their weapons - something they have repeatedly refused to do - but that Russia had no need to storm the sprawling industrial zone.
The siege of Mariupol has been the worst humanitarian catastrophe of the conflict, and has been described by Kyiv as a war crime.
Mayor Vadym Boichenko said tens of thousands of civilians had been killed there by Russian forces employing tactics of mass destruction similar to those used in campaigns in Syria and Chechnya.
Organisations such as the International Committee of the Red Cross and the United Nations say they believe thousands have been killed but the extent of suffering cannot be assessed yet because the city has been cut off.
Ukrainian officials have said around a third of the population escaped before the siege, others fled during it. President Volodymyr Zelenskiy said on Thursday that around 120,000 were still trapped inside. Many have sheltered for weeks in cellars with no power or heating, without fresh supplies of food, water or medicine.
For its part, Russia says it has taken in 140,000 civilians from the city, as well as providing humanitarian assistance. Kyiv says thousands were deported by force, in what would be a war crime, including some unaccompanied children, something Moscow denies.
Among incidents that drew international outcry was the bombing of a maternity hospital on March 9, when wounded pregnant women were photographed being carried out of rubble.
A week later, the city's main drama theatre was destroyed by bombardment. Ukraine says hundreds of people were sheltering in its basement, and it has not been able to determine how many were killed. The word "children" had been spelled out on the street in front of the building, visible from space.
Russia denies targeting civilians in Mariupol and has said, without presenting evidence, that incidents including the theatre bombing and maternity hospital attack were staged to incriminate Russia. Kyiv and its Western allies dismiss this as a smear to deflect blame.
(Writing by Peter Graff and Timothy Heritage; Editing by Kevin Liffey, Alexandra Hudson)