An injured man walks off the site of a missile strike, near the Taras Shevchenko Chernihiv Regional Academic Music and Drama Theatre (AFP via Getty Images)

At least seven people were killed and 144 injured after a Russian missile struck a theatre and a central square in the northern Ukrainian city of Chernihiv.

A six-year-old girl was among those killed and at least 15 children were wounded following the airstrike on Saturday, acting mayor Oleksandr Lomako said.

Ukrainian President Volodymyr Zelensky condemned the strike, saying Russia had turned an ordinary Saturday into “a day of pain and loss”.

“This is what a neighbourhood with a terrorist state is, this is what we unite the whole world against,” he said.

Taras Shevchenko Chernihiv Regional Academic Music and Drama Theatre was left damaged following the missile strike (Associated Press)

He added: “A Russian missile hit right in the centre of the city, in our Chernihiv.

“A square, the polytechnic university, a theatre. An ordinary Saturday, which Russia turned into a day of pain and loss.”

It came as Mr Zelensky travelled to Sweden to strengthen military and diplomatic ties between both nations.

At a joint news conference, Mr Zelensky and Swedish Prime Minister Ulf Kristersson announced that the two countries agreed to strengthen cooperation on production and training and servicing of the Swedish CV-90 infantry fighting vehicles.

As part of the agreement, CV-90 vehicles will begin production in Ukraine.

“We do not have superiority in the air, and we do not have modern aircraft. In reality, the Swedish Gripen is the pride of your country, and I believe that the Prime Minister could share this pride with Ukraine,” Mr Zelensky said, adding that “appropriate actions” would be taken in the following weeks to “open up the possibility of obtaining the appropriate aircraft.”

“I will also have negotiations with several other states tomorrow and the day after tomorrow. I am confident that we, together with our partners, will do everything and achieve the appropriate result in the sky so that the Russians do not have an advantage there,” he said.

Mr Kristersson expressed his condolences for the attack in Chernihiv. He called the Russian missile strike an “act of brutality” which “only reinforces the need for us to stand with you in all your struggles.”

Sweden abandoned its longstanding policy of military non-alignment to support Ukraine with weapons and other aid in the war against Russia.

The government says Sweden has provided 20 billion kronor (1.7 billion euros) in military support to Ukraine. Sweden also applied for NATO membership but is still waiting to join the alliance.