"We have a responsibility to prevent this conflict from escalating beyond Ukraine's borders to becoming a full-fledged war between Russia and NATO," the NATO secretary general told AFP in an interview on the sidelines of a forum in Turkey.

He warned that a no-fly zone over Ukraine would "most likely lead to a full war between NATO and Russia", causing "so much more suffering, so much more death and destruction".

Stoltenberg said a no-fly zone over Ukraine would mean that NATO would have to take out Russian air defence systems not only in Ukraine, but also around Belarus and Russia.

"It will mean that we need to be ready to shoot down Russian planes because a no-fly zone is not only something you declare you have to impose it," he told AFP at the Antalya diplomacy forum organised by Turkey.

He added that the training of tens of thousands of Ukrainian troops by NATO member states in recent years, as well as the supply of military equipment, had proved "extremely important (for Ukraine's forces) in the fight against invading Russian forces".

But he added: "The most important thing is that President (Vladimir) Putin should end this senseless war," he said.

"Withdraw all its forces and engage in good faith in diplomatic political efforts to find a political solution," said Stoltenberg.

He also praised Turkey's move to facilitate talks on Thursday between the foreign ministers of Russia and Ukraine in Antalya.

"It is important that allies continue to try to support, facilitate a political solution."