Russian President Valdimir Putin on Saturday warned the West of a wider war if a no-fly zone is set up, as his forces resumed an offensive against a key Ukrainian city where a planned evacuation of residents failed to take place over security fears.
With his Ukrainian counterpart Volodymyr Zelensky criticising NATO for ruling out a no-fly zone for fear of sparking nuclear conflict, Putin spoke of "colossal and catastrophic consequences not only for Europe but also the whole world", if such a zone was set up.
"Any movement in this direction will be considered by us as participation in an armed conflict by that country," Putin said.
For Zelensky, on day 10 of the invasion, under an escalating bombardment that has flattened more and more infrastructure and sent nearly 1.4 million civilians fleeing for their lives, the Western military alliance's "no" to a no-fly zone had essentially given "the green light for further bombing of Ukrainian cities and villages".
The strategic city of Mariupol proudly resisted Moscow-backed rebels during a 2014 conflict, but the Azoz sea port has for days been without electricity, food and water in the dead of winter and people began gathering for the evacuation.
After Russia's defence ministry declared the ceasefire -- to open a humanitarian corridor out of the war's fiercest battles -- officials said the city's 450,000-strong population could begin to leave by bus and private cars.
Since Putin's army invaded on February 24, Russia has pummelled Ukrainian cities, with officials reporting hundreds of civilians killed. Europe's largest atomic power plant has even come under attack sparking fears of a catastrophic nuclear accident.