Russian troops bore down on Ukraine’s capital Friday, with explosions and gunfire sounding in the city as the invasion of a democratic country fueled fears of wider war in Europe and triggered worldwide efforts to make Moscow stop. With reports of hundreds of casualties from the warfare — including shelling that sliced through a Kyiv apartment building and pummeled bridges and schools — there also were growing signs that Vladimir Putin’s Russia may be seeking to overthrow Ukraine’s government. It would be his boldest effort yet to redraw the world map and revive Moscow’s Cold War-era influence. NATO decided to send parts of the alliance’s response force to help protect its member nations in the east for the first time. NATO didn’t say how many troops would be deployed but added it would involve land, sea and air power. In the fog of war, it was unclear how much of Ukraine is still under Ukrainian control and how much or little Russian forces have seized. The Kremlin accepted Kyiv’s offer to hold talks, but it appeared to be an effort to squeeze concessions out of embattled President Volodymyr Zelenskyy instead of a gesture toward a diplomatic solution. Read:Explosions heard in Kyiv early Friday as Russia presses Ukraine assault The U.S. and other global powers slapped ever-tougher sanctions on Russia as the invasion reverberated through the world’s economy and energy supplies, threatening to further hit ordinary households. U.N. officials said millions could flee Ukraine. Sports leagues moved to punish Russia and even the popular Eurovision song contest banned it from the May finals in Italy. Day 2 of Russia’s invasion, the largest ground war in Europe since World War II, focused on the Ukrainian capital, where Associated Press reporters heard explosions starting before dawn and gunfire was reported in several areas. After 8 p.m., a large boom was heard near Maidan Nezalezhnosti, the square in central Kyiv that was the heart of protests which led to the 2014 ouster of a Kremlin-friendly president. The cause was not immediately known. Five explosions struck near a major power plant on Kyiv’s eastern outskirts, said Mayor Vitaly Klitschko. There was no information on what caused them and no electrical outages were immediately reported. Russia’s military said it seized a strategic airport outside Kyiv, allowing it to quickly build up forces to take the capital. It claimed to have already cut the city off from the west — the direction taken by many to escape the invasion — leading to lines of cars snaking toward the Polish border. Russia’s Defense Ministry claimed to have blocked off the cities of Sumy and Konotop and that the offensive had claimed dozens of Ukrainian military assets. The statement could not be independently confirmed. Intense gunfire broke out on a bridge across the Dneiper River dividing eastern and western Kyiv, while another key bridge to the capital was blown away. Ukrainian officials reported at least 137 deaths on their side and claimed hundreds on the Russian one. Russian authorities released no casualty figures, and it was not possible to verify the tolls. U.N. officials reported 25 civilian deaths, mostly from shelling and airstrikes, and said that 100,000 people were believed to have left their homes, estimating up to 4 million could flee if the fighting escalates. Zelenskyy tweeted that he and U.S. President Joe Biden spoke by phone and discussed “strengthening sanctions, concrete defense assistance and an antiwar coalition,” adding that he was grateful for Washington’s support. His whereabouts were kept secret after telling European leaders in a call Thursday night that he was Russia’s No. 1 target — and that they might not see him again alive. His office later released a video of him standing with senior aides outside the presidential office, saying he and other government officials would stay in the capital. “All of us are here protecting our independence of our country,” Zelenskyy said. “And it will continue to be this way. Glory to our defenders, glory to Ukraine, glory to heroes.”