Ukraine-Russia conflict: At least 7 killed, 9 wounded by shelling

Big explosions were heard before dawn in Kyiv, Kharkiv and Odesa as world leaders decried the start of an invasion that could cause massive casualties, topple Ukraine’s democratically elected government and threaten the post-Cold War balance on the continent.

Gunfire rattled near the capital's main airport, the Interfax news agency said, and sirens were heard over the city.

Russia has demanded an end to NATO's eastward expansion and Putin repeated his position that Ukrainian membership of the U.S.-led Atlantic military alliance was unacceptable.