Despite the bleak situation on the ground, NATO is unwilling to get directly involved in the conflict -- including setting up a no-fly zone -- beyond supporting Ukraine's resistance to an invasion that is killing innocent civilians.

NATO's Secretary-General, Jens Stoltenberg, said on Friday that a no-fly zone over Ukraine is not an option being considered by the alliance. "We've agreed that we should not have NATO planes operating over Ukrainian airspace or NATO troops on Ukrainian territory," he said.

What would happen if NATO imposed a no-fly zone?

The problem with military no-fly zones is that they have to be enforced by military power. If a Russian aircraft flew into a NATO no-fly zone, then NATO forces would have to take action against that aircraft. Those measures could include shooting the plane from the sky. That would, in Russia's eyes, be an act of war by NATO and would likely escalate the conflict.