Ukrainian President Volodymyr Zelenskiy appealed to Britain to do more to help his country fight Russia and to punish "the terrorist state" on Tuesday, striking a defiant tone that Ukraine would fight for its survival, no matter what the cost.

Addressing Britain's parliament and greeted by a standing ovation in a packed chamber of lawmakers, Zelenskiy documented the Russian invasion day by day, listing the weapons used, the civilians killed and those running out of food and water.

He thanked Prime Minister Boris Johnson, who has sought to take a leading role in supporting Ukraine against Russia, for the help already offered, but said Britain and other Western countries had to go further, pressing on with more sanctions. He asked them to recognise Russia as a "terrorist state".

"The question for us now is to be or not to be," Zelenskiy told parliament via videolink.

"We will not give up and we will not lose. We will fight to the end at the sea, in the air, we will continue fighting for our land, whatever the cost. We will fight in the forests, in the fields, on the shores, in the streets."

"Please increase the pressure of sanctions against this country (Russia) and please recognise this country as a terrorist state, and please make sure that our Ukrainian skies are safe... Please make sure that you do what needs to be done."

Zelenskiy has addressed his people and the world from Kyiv regularly since Russia invaded his country 12 days ago, in what President Vladimir Putin calls a "special military operation" to rid the country of leaders he characterises as neo-Nazis.

The Ukrainian leader has kept up his appeals for the West to do more to help a country he says is not only fighting for its survival but also to save democracy across the whole of Europe.

Britain has become one of Ukraine's closest allies since the invasion, with Johnson speaking frequently to him by telephone and the two, according to some, enjoy a friendly relationship.