Ukrainian forces in Severodonetsk have been ordered to withdraw, according to the top regional official.The city is the focus of Russia's invasion as it tries to take control of large parts of eastern Ukraine."Remaining in positions that have been relentlessly shelled for months just doesn't make sense," Luhansk regional head Serhiy Haidai said.Russian forces have nearly encircled Severodonetsk in recent days, and are now targeting its twin city Lysychansk."They have received orders to retreat to new positions... and from there continue their operations," Mr Haidai told Ukrainian television on Friday morning.