Russian troops have pushed further into Ukraine overnight, nearing the country's capital Kyiv on day 17 of the invasion.

The bulk of the invading force are now around 25 kilometres from the centre of the city, the UK's Ministry of Defence confirmed on Saturday morning. 

While a large number of troops north of Kyiv have dispersed, the report warned "this is likely to support a Russian attempt to encircle the city". 

Ukrainian cities of Kharkiv, Chernihiv, Sumy and Mariupol continue to endure heavy Russian shelling. 

Several humanitarian corridors are expected to open today to allow civilians to evacuate besieged cities including Mariupol, Ukraine’s deputy prime minister Iryna Vereshchuk confirmed. 

Authorities warned of a humanitarian catastrophe in the port city of Mariupol, which has been encircled by Russian forces for thirteen days and cut off from deliveries of food and medicine.

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The plans to evacuate residents follow repeated failed attempts to allow a humanitarian convoy to reach Mariupol.

Ms Vereshchuk confirmed the green corridor in a video address today. 

President Volodymyr Zelensky also accused Russian forces of kidnapping the mayor of the southern port city of Melitopol. 

Ukraine's parliament has claimed Ivan Fedorov was abducted by a group of 10 armed men who put a plastic bag over his head.

Mr Zelensky accused Russian forces "have transitioned into a new stage of terror" and equated the kidnapping to the actions of Islamic State "terrorists". 

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The prosecutor’s office of the Luhansk People’s Republic, a Moscow-backed rebel region in eastern Ukraine, said on its website that there was a criminal case against Mr Fedorov.

The prosecutor’s office accused him of “terrorist activities” and of financing the nationalist militia Right Sector to “commit terrorist crimes against Donbass civilians”. The office said it was looking for Mr Fedorov and called for anyone with information about his whereabouts to contact them.