Russian forces attempted to push into cities in eastern Ukraine have made "limited progress" in the last week, so they’ve turned instead to “indiscriminate shelling,” the UK Ministry of Defense said on Sunday.

The shelling of urban areas has caused "widespread destruction and large numbers of civilian casualties," the Ministry said in an update.

"It is likely Russia will continue to use its heavy firepower to support assaults on urban areas as it looks to limit its own already considerable losses, at the cost of further civilian casualties," the update said.

At least 847 civilians, including 64 children, have been killed in Ukraine since Russia invaded on Feb. 24, according to the United Nations.

Another 1,399 have been injured, it said.

The casualties, recorded by the Office of the United Nations High Commissioner for Human Rights, are believed to be "considerably higher" since officials have not been able to verify information in areas where there is intense fighting, the office said.

"Most of the civilian casualties recorded were caused by the use of explosive weapons with a wide impact area, including shelling from heavy artillery and multiple-launch rocket systems, and missile and air strikes," it said.

-ABC News' Jason Volack

The Kremlin confirmed Saturday that it used hypersonic missiles for the first time since invading Ukraine.

Russia used the Kinzhal aviation missile system, with hypersonic aeroballistic missiles, on the village of Delyatyn in Ukraine on Friday, according to Igor Konashenkov, a spokesman for the Russian Defense Ministry.

"On March 18, the Kinzhal aerial missile system equipped with hypersonic aero-ballistic missiles destroyed a large underground missile and air ammunition depot of the Ukrainian Armed Forces in the settlement of Deliatyn in the Ivano-Frankivsk region," Konashenkov said at a briefing on Saturday.

The Russian military claims it is capable of hitting targets at a range of more than 2,000 kilometers.

At least 562 prisoners of war are being held in Ukraine, Irina Vereshchuk, the head of the country's Ministry of Reintegration, a ministry established in 2016 to manage occupied Ukrainian territories, said in an interview with Ukrainian news service TSN on Saturday.

Vereshchuk said they are being treated according to international humanitarian law.

Ukrainian forces in Kyiv have detained 127 saboteurs, including 14 infiltration groups, since the Russian invasion began, Mykola Zhyrnov, the capital's military administration head, (told BBC)[].

All Russian troops have left the Ukrainian cities of Kyiv and Chernihiv, withdrawing north toward the borders of Belarus and Russia to consolidate before likely redeploying to the Donbas region in eastern Ukraine, a senior U.S. defense official told reporters Wednesday.

But even with the Russians gone, the territory remains treacherous.

"There are some indications that they left behind mines and things like that, so the Ukrainians are being somewhat careful in some areas north of Kyiv as they begin to clear the ground and clear the territory and re-occupy it," the official said.

While the U.S. hasn't yet seen these troops redeploy elsewhere in Ukraine, it'll likely happen soon, according to the official. Ukrainian forces are preparing for a major fight in Donbas, the official said.

The official also said the Pentagon is "monitoring" an apparent nitric acid explosion in Ukraine's Luhansk region, which Russia blamed on Ukraine.

"We've seen the Russians claim that this was a Ukrainian attack on this. We do not believe that is true," the official said. "We do believe that the Russians are responsible, but exactly what they used when they did it, why they did it, what the damage is, we just don't have that level of detail," the official said.

The official also noted that a small number of Ukrainians currently in the U.S. for "professional military education" were pulled aside for a couple days of training on Switchblade drones, which the U.S. is sending overseas as part of its military aid, according to the official.

"Although it's not a very difficult system to operate, we took advantage of having them in the country to give them some rudimentary training on that," the official said.

-ABC News' Matt Seyler