Residents of the Ukrainian capital Kyiv were urged to head to air raid shelters early on Friday as sirens wailed across the city, a day after Russia carried out the biggest aerial assault since it started the war in February. Shortly after 2.00 a.m. Kyiv's city government issued an alert on its Telegram messaging app channel about the air raid sirens and called on residents to proceed to shelters. Olekskiy Kuleba, governor of Kyiv region, said on Telegram that an "attack by drones" was under way. A Reuters witness 20 km (12 miles) south of Kyiv heard several explosions and the sound of anti-aircraft fire. Ukrainian President Volodymyr Zelenskiy, in a video address on Thursday night, said air commands in central, southern, eastern and western Ukraine repelled 54 Russian missiles and 11 drones on Thursday. Zelenskiy acknowledged that most regions were suffering power outages. The areas where loss of power was "especially difficult" included the capital Kyiv, Odesa and Kherson in the south and surrounding regions, and the region around Lviv near the western border with Poland, Zelenskiy said. "But this is nothing compared with what could have happened if it were not for our heroic anti-aircraft gunners and air defense," he said. Reuters footage on Thursday showed emergency workers searching through the smoldering wreckage of homes in Kyiv destroyed by a blast and smoke trails of missiles in the sky. Officials had earlier said more than 120 missiles were fired during Thursday's assault. More than 18 residential buildings and 10 critical infrastructure installations were destroyed in the latest attacks, the defense ministry said in a statement. Waves of Russian air strikes in recent months targeting energy infrastructure have left millions of people without power and heating in often freezing temperatures. The United States last week announced nearly $2 billion in more military aid, including the Patriot Air Defense System, which offers protection against aircraft, cruise and ballistic missiles. Landmines Britain said on Friday it has given Ukraine more than 1,000 metal detectors and 100 kits to deactivate bombs to help clear minefields. "Russia's use of landmines and targeting of civilian infrastructure underline the shocking cruelty of Putin's invasion," British defense minister Ben Wallace said in a statement. "This latest package of UK support will help Ukraine safely clear land and buildings as it reclaims its rightful territory." The metal detectors, made by German firm Vallon, can help troops clear safe routes on roads and paths by helping to remove explosive hazards, the defense ministry said, while the kits can de-arm the fuse from unexploded bombs. Wallace said on Thursday Britain would allocate 2.3 billion pounds ($2.77 billion) to Ukraine in military aid in 2023, matching the amount it has provided this year. Battlefields Moscow has repeatedly denied targeting civilians, but Ukraine says its daily bombardment is destroying cities, towns, and the country's power, medical and other infrastructure. Russia invaded Ukraine on Feb. 24 in what President Vladimir Putin calls a "special military operation" against what it perceives as threats to its security. Ukraine and its Western allies have denounced Russia's actions as an imperialist-style land grab and imposed sanctions to try to disrupt the campaign. The 11-month war has killed tens of thousands of people, driven millions from their homes, left cities in ruins and shaken the global economy, driving up energy and food prices. The heaviest fighting is in the eastern Donetsk and Luhansk provinces that together make up the industrial Donbas region. Russia claimed in September to have annexed them, along with the southern provinces of Kherson and Zaporizhzhia, but does not fully control any of them.