KYIV, Ukraine — A major Russian attack targeted Kyiv early Tuesday, injuring at least four people and heavily damaging an apartment building in the Ukrainian capital, according to witnesses and officials.Kyiv Mayor Vitali Klitschko said a suspected missile strike on a 24-story apartment building caused a collapse and people might be trapped under the rubble. Four people were injured, according to preliminary reports, he added.A fire had broken out in the Podil district on the grounds of a nonresidential property and a nine-story apartment building was on fire after debris apparently struck the roof, the mayor said.“In the Obolon district, cars are burning after being struck by falling missile debris. There are also fires at two locations in open areas, including one near a kindergarten,” Klitschko said on Telegram.Thousands of residents of Kyiv were taking refuge inside metro stations and other shelters after air raid warnings.Ukrainian President Volodymyr Zelenskyy on Monday reiterated warnings of a possible massive Russian strike and urged residents to pay special attention to air raid alerts.“Intelligence warnings regarding Russian strikes remain in effect. A massive strike is possible, they have prepared one,” Zelenskyy said in his nightly video address.“Our defenders are ready 24/7 to the fullest extent possible with the supplies currently available.”Russia last week warned that it intended to launch “systematic strikes” on targets in Kyiv linked to the Ukrainian military as well as decision-making centers and urged foreigners to leave.It said the action was in response to a drone strike last month on a dormitory in Ukraine’s Russian-held Luhansk region, which killed 21 people. Ukraine denied carrying out the attack.In Ukraine’s northeastern Kharkiv region, Gov. Oleh Syniehubov said on Telegram that at least six people were wounded, including an 11-year-old girl, in Russian shelling overnight.Reuters could not independently verify the reports.Russia has targeted Ukraine’s power supplies and infrastructure while Ukraine has stepped up attacks on oil facilities inside Russia this year, sometimes resulting in casualties. Both sides deny targeting civilians.The war in Ukraine has ground on for more than four years since Russia launched its full-scale invasion in February 2022. Efforts to end the conflict have made little progress with the U.S. administration of Donald Trump focused on conflicts in the Middle East.