Nato announced plans to beef up the defence of Europe's eastern flank on Friday, two days after Poland shot down drones that had violated its airspace in the first known action of its kind by a member of the Western alliance during Russia's military campaign in Ukraine.

Warsaw has portrayed the drone incursions as an attempt by Russia to test the capabilities of Poland and Nato to respond.

Earlier on Friday, it rejected Donald Trump's suggestion that the incursions could have been a mistake, a rare contradiction of the US president from one of Washington's closest allies.

Russia said its forces had been attacking Ukraine at the time of the drone incursions and that it had not intended to hit any targets in Poland.

"It's reckless and unacceptable. We can't have Russian drones entering allied air space," Nato Secretary-General Mark Rutte told a press conference, announcing operation "Eastern Sentry".

The mission, which begins on Friday evening, will involve a range of assets integrating air and ground bases.

Allies, including Denmark, France, Britain and Germany have so far committed to the mission with others set to join, Rutte added.

Nato's top military official, Supreme Allied Commander Europe Alexus Grynkewich, who is a US Air Force general, said the alliance would defend every inch of its territory.

"Poland and citizens from across the alliance should be assured by our rapid response earlier this week and our significant announcement here today," Grynkewich told the same press conference at Nato headquarters in Brussels.

The United Nations Security Council was set to meet on Friday at Poland's request to discuss the incident. (Reuters)