Ukraine's First Lady Olena Zelenska has issued an impassioned statement on the Russian invasion, condemning the "mass murder" of the country's civilians.

She focused on child casualties, mentioning the names of three children who had died in the bombardments.

She said Ukraine wanted peace but would defend its borders and its identity.

The whereabouts of Mrs Zelenska, 44, are unknown, and her husband President Volodymyr Zelensky says his family is a target for Russian forces.

In an open letter published on the Ukrainian president's website late on Tuesday in English, International Women's Day, Mrs Zelenska said she had received numerous requests for interviews and that her letter served as an answer.

She said the invasion was "impossible to believe. Our country was peaceful; our cities, towns and villages were full of life".

"It is, in fact, the mass murder of Ukrainian civilians," she added, despite Russian efforts to portray it as a "special operation".

"Perhaps the most terrifying and devastating of this invasion are the child casualties.

"Eight-year-old Alice who died on the streets of Okhtyrka while her grandfather tried to protect her. Or Polina from Kyiv, who died in the shelling with her parents.

"Fourteen-year-old Arseniy was hit in the head by wreckage, and could not be saved because an ambulance could not get to him on time because of intense fires.

"When Russia says that it is 'not waging war against civilians', I call out the names of these murdered children first."

But she said Russian President Vladimir Putin had underestimated Ukraine, its people and its patriotism.

"While Kremlin propagandists bragged that Ukrainians would welcome them with flowers as saviours, they have been shunned with Molotov cocktails," she added.

She also thanked people around the world for their support, and called on the West to "close the sky, and we will manage the war on the ground ourselves".

The first lady ended with a plea to media to "keep showing the truth".

"If we don't stop Putin, who threatens to start a nuclear war, there will be no safe place in the world for any of us. We will win. Because of our unity. Unity towards love for Ukraine."

Mrs Zelenska is a former screenwriter and has a high profile abroad, having accompanied her husband on several foreign trips.

She is best known in Ukraine for her campaign for better school meals and for encouraging the spread of the Ukrainian language around the world.

Mr Zelensky said near the beginning of the conflict that he was "target number one" and his family were "target number two" of the invading Russian forces.