"Russia has endangered human lives in a state that is a member of NATO and the EU," Merz said in a statement.

"This reckless action is part of a long chain of provocations in the Baltic Sea region and on NATO's eastern flank. The German government condemns this aggressive Russian action in the strongest possible terms."

Later, Merz said he had spoken on the phone with Polish Prime Minister Donald Tusk and that he shared his view that "this is a very serious threat to peace throughout Europe".

"This is a new level of attacks that we are seeing from Russia," Merz said at a press conference in Berlin.

"The Russian government's claim that this was... an accident or mistake is not credible."

Government spokesman Sebastian Hille earlier said Moscow was "testing" Ukraine's allies with the violation of Polish airspace, which he called a "very serious" incident.

Hille said it "once again shows the threat that we face" and how much Germany and other NATO countries "are being tested by Russia".

Defence Minister Boris Pistorius told parliament the drones were "clearly set on this course" and "did not have to fly this route to reach Ukraine".

"There is absolutely no reason to believe that this was a course correction error or anything of the sort," Pistorius said.

According to Polish sources, the drones were "suitably armed", the defence minister added. "So something could have happened at any time."

Foreign Minister Johann Wadephul said Russia had "carelessly risked a dangerous escalation" with drones entering Polish airspace "on a significant scale".

He added: "Russia must know that NATO is capable of action and that it will react to defend NATO territory."

Poland was gathering its NATO allies for urgent talks Wednesday after the Russian drones flew into its airspace during an overnight attack on Ukraine.

Tusk said he had invoked NATO's Article 4 under which a member can call urgent talks when it feels its "territorial integrity, political independence or security" are at risk.

Pistorius said Germany was cooperating with Poland in the form of consultations under Article 4, saying: "We support this approach, which we consider to be correct."