Meet the young Ukrainians defending their country’s front lines

American citizens in Ukraine are being urged to leave the country due to an “increased threat of Russian military action”.

The warning from the US embassy in Kyiv comes as western leaders have repeated warnings that Russia would pay a heavy price for invading.

Moscow meanwhile has accused the west of following “an aggressive course” and has denied it plans to enter Ukraine.

We report from the Ukrainian port city of Mariupol in the south-east of the country, close to the Russian border.