After Russian forces surrounded the city of Mariupol in southern Ukraine, cutting off its water and fuel and preventing aid convoys from entering, Yulia Beley sheltered in a neighbor's basement with her three daughters.

She ventured out as bombs rained down to fetch water from a distant well and try to comfort her children while the shelling shook the walls and ceiling. Ms. Beley said she fed her hungry children one bowl of porridge a day. Her daughter dreamed of the sweet rolls her mother made before the war.

Ms. Beley, who escaped from the city a week ago, said it tears her apart.

Russia tried to starve the city of Mariupol into submission after it invaded Ukraine.

Women pushing mostly empty shopping carts near a damaged block of apartments in Mariupol on March 17. Residents have struggled to find food and water since Russian troops laid siege to the city.Credit...Alexander Ermochenko/Reuters

Throughout history, armies have used sieges regardless of the effects on civilians in the middle.

The Secretary of State accused Russia of starving cities in Ukraine. The brother of President Putin died in infancy during the German siege of Leningrad during World War II.

The world is saying to Russia: stop these attacks immediately. Allow the food and medicine to enter. Let the people leave and end the war against Ukraine.

The tactic of siege warfare can be used to weaken enemies while avoiding battles that can kill the besieging force, or to freeze active fronts while attacking forces. sieges have a psychological power that is unique to war tactics, according to scholars and siege survivors.

Syrians displaced from Eastern Ghouta, near Damascus, waiting to receive food at a shelter in Horjelli, Syria, in 2018.Credit...Hassan Ammar/Associated Press

She said that bombarding a residential area of food serves not only to flush out combatants, but to communicate to everyone trapped inside. You don't deserve to eat, drink, or have medicine.

Russian forces cut off Mariupol from everything it needed to live after they surrounded it, the mayor said. The city's power plants were destroyed, cutting off electricity to residents as temperatures plummeted.

Some civilians were able to flee through destroyed streets and Russian checkpoints. More than two dozen buses that were sent to evacuate people from the city have not been able to enter because of Russian shelling.

The warring parties could not guarantee the safety of aid workers, so the International Committee of the Red Cross stopped relief operations in Mariupol on Monday.

Residents lined up for hot food in an improvised bomb shelter in Mariupol on March 7.Credit...Evgeniy Maloletka/Associated Press

The mayor estimated that almost 5,000 people have been killed there, but the figures could not be confirmed because of the difficulty of getting information.

Russian forces are in control of parts of Mariupol, according to the President of Ukraine. According to Ukrainian and British military assessments, the center of the city continues to hold.

An aide to the mayor told The New York Times that the city was being defended by thousands of Ukrainian fighters.

When the siege began, one Mariupol resident, Kristina, said she, her husband and two children camped out in the entryway of their building, hoping it would provide better shelter and protection than their apartment.

She cooked on an open fire while her husband searched for water. They boiled the water to make it sterile.

An armored convoy of pro-Russian troops filled a road leading to Mariupol on Monday.Credit...Alexander Ermochenko/Reuters

She read fairy tales to distract the children, but once they got hungry, the fire was gone from their eyes.

She said that they ate once a day.

Her father and grandparents were left behind when her family fled the city. The city's phone networks are mostly out, so she has had a hard time keeping up with them.

She said that last week they sent a text that said: "No roof, no food and no water."

Doctors who study hunger and starvation describe a grim process of the body mining itself to stay alive. The first thing it does is burn the sugar in the body.

Residents passed by a fallen electricity pylon and a destroyed apartment building in Mariupol on March 25.Credit...Alexander Ermochenko/Reuters

An adult can survive for more than 70 days on water alone if they are well-fed. The elderly and the ill are more likely to die quickly.

Research shows that starving weakens the body and disturbs the mind.

According to Nancy Zuker, a professor of psychiatry and behavioral sciences at Duke University, research done during World War II on 36 male conscientious objectors who ate a low calories diet modeled on that given to prisoners of war showed they had suffered significant psychological consequences.

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There are ongoing peace talks. Russia said that it would reduce military activity in the area. The announcement was the first sign of progress from the peace talks.

On the ground. Russia gave up some territory in the north of the country, which was a result of a successful Ukrainian resistance.

Biden's comments. President Biden said that Putin cannot remain in power. On Monday, Mr. Biden said that his remark was a personal expression of his moral outrage.

They had increased anxiety, increased isolation, and depression.

It compounds in traumatic circumstances.

She said that it was hard to separate the psychological consequences of being in a state of war from those of not having enough food.

Residents gathered water at a well on the outskirts of Mariupol on March 9.Credit...Evgeniy Maloletka/Associated Press

The conscientious objectors were haunted by the memory of hunger after they regained their strength.

She said that they needed to be surrounded by food.

The municipal worker from Mariupol said that she could not eat for days after she escaped.

She began to crave a full meal every hour after that.

An hour passes and you want to eat. You want to eat as much as you can.

She said she was confused at first.

I see that my body is fighting back.

An apartment building hit by shelling in Mariupol, on March 7.Credit...Evgeniy Maloletka/Associated Press

Bombs and shells were so common in Mariupol that Ms. Beley's daughter, Aida, 3, learned to distinguish between incoming and outgoing fire.

The family ran out of food. A woman gave her a jar of honey.

She said that they didn't have food, but they did eat.

She felt weak when her family finally escaped. She initially refused the candy offered by the Russian soldiers. Then she changed her mind again.

She said that she needed something so that she could maintain herself.

Ms. Beley’s daughter Diana, 11, on a phone with her friends Kira and Liza at the shelter in Lviv. Credit...Mauricio Lima for The New York Times

Ben Hubbard from Lebanon, Asmaa al-Omar from Lebanon, and Gina Kolata from N.J. all reported from Lebanon.