Russia pressed its invasion of Ukraine to the outskirts of the capital Friday after unleashing airstrikes on cities and military bases and sending in troops and tanks from three sides in an attack that could rewrite the global post-Cold War security order.

Explosions sounded before dawn in Kyiv and gunfire was reported as Western leaders scheduled an emergency meeting and Ukraine’s president pleaded for international help to fend off an attack that could topple his democratically elected government, cause massive casualties and damage global economy. The UN said 25 civilians died. The military said Friday that Russian spies and saboteurs were seen on the outskirts of Kyiv, and police told people not to exit a subway station because there was gunfire in the area. Elsewhere in Kyiv, soldiers established defensive positions at bridges, and armoured vehicles rolled down streets, while residents stood uneasily in doorways of their buildings. US Secretary of State Antony Blinken said Kyiv “could well be under siege” in what US officials believe is a brazen attempt by Russian President Vladimir Putin to install his regime.