KYIV, Ukraine (AP) — Russian forces showered Ukraine with more missiles and munition-carrying drones Tuesday after widespread strikes killed at least 19 people in an attack the UN human rights office described as “particularly shocking” and amounting to potential war crimes.

Air raid warnings sounded throughout Ukraine for a second-straight morning as officials advised residents to conserve energy and stock up on water. The strikes have knocked out power across the country and pierced the relative calm that had returned to Kyiv and many other cities far from the war’s front lines.

“It brings anger, not fear,” Kyiv resident Volodymyr Vasylenko, 67, said as crews worked to restore traffic lights and clear debris from the capital’s streets. “We already got used to this. And we will keep fighting.”

The leaders of the Group of Seven industrial powers condemned the bombardment and said they would “stand firmly with Ukraine for as long as it takes”. Their pledge defied Russian warnings that Western assistance would prolong the war and the pain of Ukraine’s people.

Russia launched the widespread attacks in retaliation for a weekend explosion that damaged the Kerch Bridge between Russia and the Crimean Peninsula, which Moscow annexed in 2014. Russian President Vladimir Putin alleged that Ukrainian special services masterminded the blast. The Ukrainian Government has applauded it but not claimed responsibility.

Ukrainian President Volodymyr Zelenskyy urged the G-7 leaders during a virtual meeting to respond “symmetrically” to the attacks on the Ukrainian energy sector by doing more to stop Russia from profiting off its exports of oil and gas.

“Such steps can bring peace closer,” he said. “They will encourage the terrorist state to think about peace, about the unprofitability of war.”

Ukrainian officials said the diffuse strikes on power plants and civilian areas made no “practical military sense”. However, Putin’s supporters had urged the Kremlin for weeks to take tougher action in Ukraine and criticised the Russian military for a series of embarrassing battlefield setbacks.

Pro-Kremlin pundits lauded the attacks as an appropriate and long-awaited response to Kyiv’s successful counter-offensives. Many of them argued that Moscow should keep up the intensity to win a war now in its eighth month.

The head of Britain’s cyber-intelligence agency, Jeremy Fleming, said Tuesday in a rare public speech that Russia is running out of military supplies and struggling to fill its ranks.

“Russia’s forces are exhausted,” Fleming said. “The use of prisoners as reinforcements, and now the mobilisation of tens of thousands of inexperienced conscripts, speaks of a desperate situation.”

Like Monday’s strikes, the bombardment Tuesday struck both energy infrastructure and civilian areas. One person was killed when 12 missiles slammed into the southern city of Zaporizhzhia, setting off a large fire, the State Emergency Service said. A local official said the missiles hit a school, residential buildings and medical facilities.

Energy facilities in the western Lviv and Vinnytsia regions also took hits. Officials said Ukrainian forces shot down an inbound Russian missile before it reached Kyiv, but the capital region experienced rolling power outages as a result of the previous day’s strikes.

The governor of Mykolaiv, Vitaliy Kim, urged residents to remain in bomb shelters as “there are enough missiles still in the air”.

The State Emergency Service said 19 people died and 105 people were wounded in Monday’s strikes. At least five of the victims were in Kyiv, Mayor Vitali Klitschko said. More than 300 cities and towns lost power.

A spokesperson for the office of the UN high commissioner for human rights said Tuesday that strikes on “civilian objects”, including infrastructure such as power plants, could qualify as a war crime.

“Damage to key power stations and lines ahead of the upcoming winter raises further concerns for the protection of civilians and in particular the impact on vulnerable populations,” Ravina Shamdasani told reporters in Geneva. “Attacks targeting civilians and objects indispensable to the survival of civilians are prohibited under international humanitarian law.”

War crimes investigations have long been underway in towns where mass graves were found, along with other evidence of atrocities, after they were liberated from Russian occupation. In Lyman, a city in the eastern Donetsk region, forensic workers pulled several bodies from a mass grave Tuesday, part of an arduous effort to piece together evidence of what happened under more than four months of Russian occupation. Regional Governor Pavlo Kyrylenko said the bodies of 32 Ukrainian soldiers have been exhumed so far from one mass grave.

The tempo of the war in the last month fanned concerns that Moscow might broaden the battlefield and resort to using nuclear weapons in Ukraine. As Ukraine’s counter-offensives in the east and south forced Russia’s troops to retreat from some areas, a cornered Kremlin ratcheted up Cold War-era rhetoric.

Russian Foreign Minister Sergey Lavrov said Tuesday that Moscow would only employ nuclear weapons if the Russian State faced imminent destruction. Speaking on State TV, he accused the West of encouraging false speculation about the Kremlin’s intentions.

Russia’s nuclear doctrine envisions “exclusively retaliatory measures intended to prevent the destruction of the Russian Federation as a result of direct nuclear strikes or the use of other weapons that raise the threat for the very existence of the Russian state,” Lavrov said.