Several explosions have rocked the centre of Kyiv.
Witnesses in the Ukrainian capital suggest they appear to be the result of missile strikes.
Emergency services say there have been deaths.
Blasts have also been reported in the cities of Lviv and Dnipro.
It comes after Vladimir Putin accused Ukraine of 'terrorism' - he blames the country for an explosion on a bridge linking Russia to Crimea.
President Volodymyr Zelenskyy's called the attack "absolute evil."
In a post on Telegram, he said:
"They are trying to destroy us and wipe us off the face of the earth. In general."
"Destroy our people who are sleeping at home in Zaporizhzhia."
He continued, saying there are "dead and wounded" and urged citizens not to leave their bomb shelters.
"Let's hold on and be strong."
Sky's defence and security editor Deborah Haynes says today's assault is a worrying development.
"You'll remember the Capital came under heavy bombardment at the start of the war."
"But there's been relative calm there for several months."
"So this is very unsuual - to have strikes right in the heart of the city."