As Russian troops continue their assault on Ukraine, the humanitarian situation on the ground, particularly in besieged population centers like Mariupol, is becoming increasingly dire. Ceasefire violations mean there is no safe corridor for evacuations in many areas, while attacks on critical infrastructure have cut out heat, electricity, and water in some places. Critical supplies are also becoming dangerously scarce.

Such shortages, as the war enters its third week, reflect a burgeoning humanitarian crisis — one that could grow far worse for Ukrainians who now have little prospect of escaping already besieged cities.

The strategies behind the crisis, though, are considered a common element of Russian siege warfare tactics, according to Rita Konaev, the associate director of analysis at Georgetown University’s Center for Security and Emerging Technology, which are likely to spread as the war moves into a new phase.

Already, the steady bombardment of cities is damaging civilian infrastructure, such as the hospital maternity ward in Mariupol that was struck just this week, killing three. In Kharkiv, Ukraine’s second-largest city, a care home for those with disabilities was reportedly shelled on Friday.

Localized damage can have city-wide implications. According to Konaev, many cities are reliant on a “pretty fragile grid system of life-saving and life-necessity utilities. If you damage one pipe, it can damage water access or heating for thousands of people.”

And mounting outages pose a growing threat: In Mariupol, a strategic port city in southern Ukraine, residents have gone without heat, water, and electricity for more than a week due to Russian bombardment.

On Friday, Ukrainian President Volodymyr Zelenskyy announced renewed attempt to get critical humanitarian aid to the city. “Russian troops did not let our aid into the city and continue to torture our people, our Mariupol residents,” he said. “We will try again.”

Dispatches from Mariupol, though, capture a city already in crisis.

“All the shops and were looted five to four days ago,” Sasha Volkov, deputy head of the International Committee of the Red Cross (ICRC) in Mariupol, said in a video posted to Twitter. “People report varying needs in medicine, especially for diabetes and cancer patients. But there is no way to find it anymore in the city.”

Audio posted by the aid group Médecins Sans Frontieres (MSF) from Mariupol is equally dire.

“There is no drinking water and any medication for more than one week, maybe even 10 days, without drinking water and medication,” a local aid worker says in the recording. “There’s no places where we can find food, or even [drinkable] water.”

On Wednesday, Mariupol Deputy Mayor Serhiy Orlov told journalists in a panel discussion that the water crisis in Mariupol is so acute that a 6-year-old child had died of dehydration. That claim has not been independently verified, however.

According to MSF staff, Mariupol residents have started looking for sources of groundwater, and drinking it after boiling over a wood fire, since there’s no electricity or fuel to cook.

The lack of heating is also a major problem for the city’s besieged residents: Nighttime temperatures there have consistently fallen below freezing, according to the AP.

So far, according to Orlov, aerial bombardment in Mariupol has caused the majority of civilian casualties there. As Konaev told Vox earlier this month, it’s all part of a grim strategy.

“The Russian approach to urban warfare very much emphasizes priming and prepping the ground for any sort of ground operation with this destruction from the air,” she said. “It’s to break morale, it’s to cause significant damage to the infrastructure of cities, it’s to cause high levels of displacement from the cities.”

On Wednesday, Orlov described the bombardment as a war crime.

“Putin wants to get the city regardless of the casualties and damage,” he said. “The city is being brought back to the medieval times by the Russians. People can cook only by fire, and mothers and newborn children are not getting food. This is a genocide against Ukrainians.”

Civilians are running out of supplies — but can’t escape besieged cities

While the humanitarian situation in Mariupol is dire, it is by no means the only Ukrainian city suffering from Russia’s brutal urban warfare tactics.

Kharkiv, a city in northeastern Ukraine just miles from the Russian border, has been subject to constant aerial bombardment since the start of the war, which, according to Mayor Ihor Terekhov, has rendered 400 residential buildings in the city uninhabitable. Critical infrastructure, like water supplies and heating facilities serving Kharkiv’s 1.4 million residents, have been damaged as well.

While evacuations are ongoing, Terekhov said, doing so is extremely dangerous due to the bombings.

Already, more than 2.5 million people have fled Ukraine, creating Europe’s largest refugee crisis since World War II.

Kharkiv is considered an important Russian target because of its geographical proximity to Russia, as well as a large Russian-speaking population and its history as the USSR-dominated capital of the Ukrainian Soviet Socialist Republic in the 1910s and 1920s, when Ukraine was fighting for independence from the Russian empire and its successor state.

The cities of Sumy and Trostyanets in northeastern Ukraine, near the Russian border, are both facing a critical shortage of food and medicine. “We need to establish an external supply of aid,” Sumy Mayor Oleksandr Lysenko said during the same panel discussion Wednesday.

“There are practically no stocks left in the city,” he said, adding that the city had either given away or sold its food stores, and that there was a critical shortage of insulin and antibiotics. Trostyanets Mayor Yuri Bova told journalists that while the hospital there is functioning, it’s running out of supplies. “We need to bring in medication and food,” he said.

Mariupol is facing similar shortages: Orlov said the most critical needs in his city were medicine — in particular insulin — warm clothes, and fuel. “I would not have imagined this in my worst nightmare,” he said, describing the situation on the ground. “Let me make it clear … we have total destruction of the city of Mariupol.”

However, Russian troops have encircled both Mariupol and Trostyanets and are approaching Sumy, making it nearly impossible to bring supplies in — and making humanitarian evacuation extremely dangerous. Lysenko said that while people have been trying to leave Sumy via so-called “green” corridors, “there have been times when tanks have shot at civilian vehicles trying to leave.”

Lysenko’s specific claim has not been independently verified, but civilian casualties among evacuees are well-documented; a family of three was killed by a Russian shell near Kyiv earlier this month while attempting to evacuate, along with a volunteer assisting the family.

The shortage of medicines has reached Kyiv as well, according to a Washington Post report. Long lines at pharmacies for essential medications like insulin — and even aspirin — are the norm as shipments from outside the city have been cut off due to the Russian military’s advance on the city.

“This is a problem of the last kilometers, where you need to bring your supply in the open conflict area,” Carla Melki, the emergency coordinator for MSF in Odessa, told the Post. “We know where the needs are; it’s how to reach them.”

Ad hoc groups of volunteers have coordinated to provide medications and call pharmacies to check on supplies for those who are unable to stand in line and wait, and the ICRC has delivered stores of insulin to Odessa and Dnipro, while the Ukrainian government said it had sent more than 440 tons of medical supplies to cities since the beginning of the war, the Post reports.

Even if humanitarian aid can get to besieged cities and ceasefires allow for safe evacuations — which is by no means a sure thing — the desperation Ukrainian cities are experiencing right now, less than three weeks into the war, forebodes further suffering for civilians in Ukraine.

As Orlov noted, Russian airstrikes are currently the major cause of civilian injury and death. The situation in Mariupol shows that second-order crises caused by a Russian siege can be equally catastrophic, however, creating an excruciating choice for many Ukrainians: Stay and risk death by starvation or disease, or try to flee and risk the same fate by Russian artillery.