Ukrainian President Volodymyr Zelenskyy has consistently called for a no-fly zone, but NATO allies are resisting the move, which could drag them into war with Russia.

Speaking ahead of a meeting at NATO headquarters in Brussels, Lithuania said the alliance would be dragged into war if it imposed a no-fly zone.

Canadian Foreign Minister Melanie Joly said NATO's red line was not to provoke a wider international conflict but that all scenarios needed to be discussed, Reuters reported.

The French presidential administration has described the no-fly zone as "a very legitimate request and very difficult to satisfy."

Securing a no-fly zone over Ukrainian airspace would force NATO aircraft to directly confront Russian aircraft, risking dragging the alliance into an open conflict that spills over into Europe. The prospect of a war that would extend beyond Ukraine is very worrying for Eastern European states, Bloomberg wrote.

“No-fly zone means NATO being in a conflict since it would be NATO's forces enforcing this no-fly zone,” the Czech Republic's Foreign Minister Jan Lipavsky told reporters ahead of a meeting of alliance ministers.

Allies are also concerned that NATO does not have the means to close the skies over Ukraine, given Russia's strong military capabilities. 

"NATO is not part of the conflict," Stoltenberg told reporters on Friday. "NATO is a defensive alliance, We don't seek war, conflict with Russia."

Pentagon spokesman John Kirby also rejected Ukrainian calls for a no-fly zone, saying it would only exacerbate the conflict and turn it into a war between the US and Russia.