Russia has widened its strikes on civilian infrastructure in Ukraine in the past week and is likely to expand its target range further, Britain said on Sunday, while Ukrainians returning to territory abandoned by Russian forces tried to find their dead.

Five civilians were killed in Russian attacks in the Donetsk region over the past day, while in Nikopol several dozen high-rise and private buildings, gas pipelines and power lines were damaged by Russian strikes, the governors of those regions said separately on Sunday.

On Saturday, Ukrainian President Volodymyr Zelenskiy said investigators had discovered new evidence of torture used against some soldiers buried near Izium, one of more than 20 towns that were retaken in the northeastern Kharkiv region after a lightning advance by Ukraine’s forces earlier this month.

Zelenskiy said in a video address that authorities had found a mass grave containing the bodies of 17 soldiers in Izium, some of which he said bore signs of torture.

Residents of Izium have been searching for dead relatives at a forest grave site discovered last week and where emergency workers have begun exhuming bodies. The causes of death for those at the grave site have not yet been established, although residents say some died in an airstrike.

Ukrainian officials said last week they had found 440 bodies in the woodlands near Izium. They said most of the dead were civilians and that the site proved war crimes had been committed by Russian invaders who occupied the area for months.

Oleksandr Ilienkov, the chief of the prosecutor’s office for the Kharkiv region, told Reuters at the site on Friday: ”One of the bodies (found) has evidence of a ligature pattern and a rope around the neck, tied hands,” adding that there were signs of violent death causes for other bodies but they would undergo forensic examination.

Valery Marchenko, mayor of Izium, told state television on Sunday that ”the exhumation is underway, the graves are being dug up and all the remains are being transported to Kharkiv”.

He added, "the work will continue for another two weeks, there are many burials. No new ones have been found yet, but the services are looking for possible burials".

Moscow regularly denies committing atrocities in the war or deliberately attacking civilians. The Kremlin has not commented publicly on the discovery of the graves.

The head of the pro-Russian administration that abandoned the area earlier this month accused Ukrainians of staging the atrocities at Izium. ”I have not heard anything about burials,” Vitaly Ganchev told Rossiya-24 state television.

Russian President Vladimir Putin has not responded to the accusations but on Friday brushed off Ukraine’s swift counteroffensive, casting Russia’s invasion as a necessary step to prevent what he said was a Western plot to break Russia apart.

In an intelligence update on Twitter, Britain’s Ministry of Defence said that Russia had lauched several thousand long-range missiles against Ukraine since the start of the invasion.

”However, in the last seven days Russia has increased its targeting of civilian infrastructure even where it probably perceives no immediate effect,” the ministry said in the tweet.

The strikes have struck targets including an electricity grid and a dam, it added.

”As it faces setbacks on the front lines, Russia has likely extended the locations it is prepared to strike in an attempt to directly undermine the morale of the Ukrainian people and government,” the ministry said.

BIDEN WARNS RUSSIA

Putin has said Moscow would respond more forcefully if its troops were put under further pressure, raising concerns he could at some point use unconventional means like small nuclear or chemical weapons.

U.S. President Joe Biden asked what he would say to Putin if he was considering using such weapons, replied: ”Don’t. Don’t. Don’t. It would change the face of war unlike anything since World War Two.” He made the comment in an interview with CBS programme ”60 Minutes”, a clip of which was released by CBS on Saturday.

Some military analysts have said Russian might also stage a nuclear incident at the Russian-held Zaporizhzhia nuclear power plant, Europe’s largest.

Russia and Ukraine have blamed each other for shelling around the plant that has damaged buildings and disrupted power lines needed to keep it cooled and safe.

One of the plant’s four main power lines has been repaired and is once again supplying the plant with electricity from the Ukrainian grid, the United Nations nuclear watchdog said on Saturday.

Ukraine has also launched a major offensive to recapture territory in the south, where it hopes to trap thousands of Russian troops cut off from supplies on the west bank of the Dnipro River, and retake Kherson. Kherson is the only large Ukrainian city Russia has captured intact since the start of the war.