The people of the second-largest city in the country, Kharkiv, have been told to shelter indoors.

In a statement on Sunday morning, the governor of Kharkiv told people not to leave their homes after a break through of light equipment of the Russian enemy.

Sky News verified a video that shows tanks driving into the city, which is just 20 miles south of the Russian border.

Russian troops blew up a nine-story residential block, killing an elderly woman.

The building was badly damaged, but around 60 residents were spared injury after taking refuge in the basement.

Russian forces blew up a major gas line in the city, which the Ukrainian government said could cause an environmental catastrophe. The residents were told to cover their windows with cloth.

A group of scientists from the Nationwide Academy of Sciences of Ukraine are in the city of Kharkiv.

They wrote in an email that a kindergarten and a hospital had been bombed and children killed. They are on the gas pipes of high-rise buildings. They said that this is an absolute horror and a reality that is hard to believe.

On the fourth day of the invasion, there were attacks.

In a brief televised address this morning, Putin saluted the bravery of Russian special forces fighting in Ukraine.

He referred to the invasion as a special operation to provide assistance to the people of the Donbas.

Insider's live blog is covering developments as they happen.