KYIV, Feb 25 (Reuters) - Missiles pounded the Ukrainian capital on Friday as Russian forces pressed their advance and Ukrainian President Volodymyr Zelenskiy pleaded with the international community to do more, saying sanctions announced so far were not enough.

Air raid sirens wailed over the city of 3 million people, where some were sheltering in underground metro stations, a day after Russian President Vladimir Putin launched an invasion that has shocked the world. A Ukrainian official said a Russian plane had been shot down and crashed into a building.

A senior Ukrainian official said Russian forces would enter areas just outside the capital, Kyiv, later on Friday and that Ukrainian troops were defending positions on four fronts despite being outnumbered.

An estimated 100,000 people fled as explosions and gunfire rocked major cities. Dozens have been reported killed. Russian troops seized the Chernobyl former nuclear power plant north of Kyiv as they advanced on the city from Belarus.

U.S. and Ukrainian officials say Russia aims to capture Kyiv and topple the government, which Putin regards as a puppet of the United States.

Zelenskiy said he understood Russian troops were coming for him but vowed to stay in Kyiv.