At least 1,119 civilians have been killed and 1,790 others have been injured in Ukraine since Russian forces invaded on Feb. 24, according to the latest figures from the Office of the United Nations High Commissioner for Human Rights (OHCHR).

At least 99 children were among the dead, according to the OHCHR, which noted that the Prosecutor General's Office of Ukraine had reported at least 139 children were killed as of Sunday.

"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," the agency said in a statement Sunday.

The agency noted that the actual number of casualties are believed to be "considerably higher" because the receipt of information from some areas with intense hostilities, like the southeastern port city of Mariupol, have been delayed and many reports are still pending corroboration.

Other areas where the number of casualties are still being corroborated include Volnovakha in the Donetsk Oblast, Izium in the Kharkiv Oblast, Popasna and Rubizhne in the Luhansk Oblast, and Trostianets in the Sumy Oblast, where there are allegations of numerous civilian casualties, according to the OHCHR. Casualty numbers from these regions are not included.

The nightly citywide curfew in Ukraine's capital, Kyiv, has been shifted back and shortened by an hour.

Starting Monday night, the curfew will be from 9 p.m. to 6 a.m. local time.

There has been a curfew in Kyiv every day since the start of the Russian invasion on Feb. 24. The previous time frame was from 8 p.m. to 7 a.m. local time.

-ABC News' Julia Drozd and Patrick Reevell

Russian forces on Monday morning were attempting to breach defenses from the northwest and east of Ukraine to seize key highways and settlements, which are held by Ukrainian troops, according to Ukrainian officials.

Meanwhile, Ukrainian officials said that hypersonic missiles for the Russian military's Iskander-M short-range ballistic missile system were being delivered to the Belarusian town of Kalinkovichi. Two of the latest strikes to hit Lutsk, a city in northwestern Ukraine, were launched from neighboring Belarus, according to Ukrainian officials.

-ABC News' Julia Drozd

Ukraine and Russia have both said that a new round of peace negotiations with be held in person in Turkey at the start of this week, but it remains unclear whether the talks begin Monday or Tuesday.

One of the Ukrainian negotiators, David Arakhamia, has said the talks would be held Monday through Wednesday.

Russia's lead negotiator, Vladimir Medinsky, has said the talks would start Tuesday.

Arakhamia said the decision to hold the negotiations in person was reached during the latest round of talks via video link, which are taking place everyday.

Ukrainian President Volodymyr Zelenskyy has told Russian journalists that his country is ready to compromise on Moscow's demand for neutral status, but wants meaningful security guarantees from Western countries. He said any peace deal is only possible if Russia withdraws all of its troops to areas occupied before the war began.

-ABC News' Patrick Reevell

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