Kyiv, Ukraine (cypher blog)The southeastern Ukrainian city of Mariupol came under siege from Russian forces Thursday, as Moscow sought to tighten its grip on the south of the country and the humanitarian crisis appeared to dramatically worsen.
City authorities warned of a "critical" situation for residents who are trapped under heavy shelling without power, heating or water. It's not clear how many of Mariupol's roughly 400,000 inhabitants have been able to evacuate the port city or how many have been killed or injured.
The Russian assault on Mariupol comes as its forces also fight for control of the Black Sea city of Kherson. The mayor of Kherson indicated overnight that Russian forces had seized control of the city of about 300,000, although claims remain disputed.
The advance in Ukraine's south show Russian forces are attempting to create the beginning of a potential land bridge that could link the port city of Odessa in the west, through Kherson and Mariupol to the separatist-held pro-Moscow territories in the east.

Mariupol's deputy mayor Sergei Orlov told CNN's "New Day" the city was now "surrounded" by Russian forces and was in desperate need of military and humanitarian aid.
"Our Ukrainian army and National Guard is very brave, they stand and fight for Ukraine, for Mariupol. But the situation is quite critical," Orlov said Thursday.
"We are asking for help, for military help, and we are waiting for military help," Orlov said. "Our internal forces are very brave, but we are surrounded by the Russian army, which has more people in their army."
He warned that the city was facing a humanitarian crisis after what he said had been 26 hours of continued shelling.
"They are destroying our city with all weapons, from artillery, from airplane bombing, from tactical rockets, from multiple launch rocket systems," Orlov said.
"We do not have electricity in the whole city, we do not have water supplies, we do not have sanitary systems, we do not have heating."
Smoke rises from an air defense base in the aftermath of an apparent Russian strike in Mariupol on February 24, 2022.
Smoke rises from an air defense base in the aftermath of an apparent Russian strike in Mariupol on February 24, 2022.
Mariupol's mayor Vadym Boichenko accused the Russian military of creating a "humanitarian catastrophe" in the city in a post on his Telegram account Thursday.
"These scum have found no other way to break us. They are blocking the supply and repair of electricity, water and heat. They have also damaged the railways. They have destroyed bridges and smashed trains so that we can't evacuate women, children and the elderly out of Mariupol," he said.
"They are blocking food supplies, blocking us like in former Leningrad [during World War II], deliberately destroying the city's critical life-support infrastructure for seven days. Again, we have no light, water or heat."
He said the city was "working with international institutions to create a 'green corridor' for the humanitarian mission" and seeking to get a ceasefire so electricity supplies can be restored.The Russian military announced advances in the Mariupol area Thursday morning.
"The units of the armed forces of the Donetsk People's Republic narrowed the encirclement of the city of Mariupol, and also took control of the settlements of Vinogradnoye, Sartaka and Vodyanoye," Maj. Gen. Igor Konashenkov, the Russian Ministry of Defense spokesman, said in a video briefing. He repeated claims the military was not targeting civilian areas in Ukraine.
A day earlier, Konashenkov outlined an evacuation corridor from Mariupol. "All civilians wishing to leave Mariupol, for security purposes, can go east along the Mariupol-Shirokino [Shyrokyne] road," he said.
Russia routinely denies causing civilian casualties in Ukraine. However, CNN and other media and observers have extensively documented civilian casualties and damage to civilian infrastructure.
A woman reacts as paramedics perform CPR on a girl who was injured during shelling, at the city hospital of Mariupol on February 27, 2022. The girl did not survive.
A woman reacts as paramedics perform CPR on a girl who was injured during shelling, at the city hospital of Mariupol on February 27, 2022. The girl did not survive.
Orlov said that Russian shelling had targeted multiple civilian buildings, including homes, kindergartens and schools, but he cautioned that the civilian death toll in the city remains unclear.
"We do not know how many, because we cannot collect all the bodies and we cannot count," Orlov said.
Mariupol lies just to the west of the Donbas area of eastern Ukraine that has been controlled by Russian-backed separatists since 2014. The Russian government recognized the breakaway statelets of the Donetsk and Luhansk People's Republics in the Donbas last month.
It is quite clear that Putin is pushing for a land corridor to Crimea. I mean that is an obvious objective," NATO's former Deputy Supreme Allied Commander for Europe Richard Shirreff told CNN. Russia illegally annexed Ukraine's Crimean peninsula in 2014.
Shirreff said he feared the latest push could cause a humanitarian catastrophe as civilian deaths rise and cities become ruins.