NATO's secretary-general apologised to Turkey on Friday over military exercises in Norway during which Turkey's founding leader, Mustafa Kemal Ataturk, and current president, Recep Tayyip Erdogan, were reportedly depicted as “enemies.”

Erdogan said Turkey withdrew 40 of its soldiers participating in the drills at NATO's Joint Warfare Centre in Stavanger, Norway, in protest of the incident and slammed the alliance.

“There can be no such unity, no such alliance,” he said in an address to his ruling party's provincial leaders.

Nato Secretary-General Jens Stoltenberg issued a statement saying: “I apologise for the offence caused.”

He said the incident was the result of an “individual's actions” and didn't reflect the views of the alliance.

The individual, described as a civilian contractor seconded by Norway and not a Nato employee, was removed from the exercise and an investigation was underway, Stoltenberg said.

“It will be for the Norwegian authorities to decide on any disciplinary action,” Stoltenberg added. “Turkey is a valued Nato ally, which makes important contributions to allied security.” Erdogan said Ataturk's picture and his own name were featured on an “enemy chart” during the drills.

The Joint Warfare Centre is a multi-national Nato unit based in Stavanger, 300 kilometers southwest of Oslo. It is currently led by Maj Gen Andrzej Reudowicz of Poland. According to its website, it has a staff of 250 made up of civilians from 11 Nato member states, including Turkey.

In March, the Norwegian government caused fury in Turkey by granting political asylum to five Turkish officers based in Norway who had refused to return home after the failed July 2016 coup attempt in Turkey.

The five officers said that they feared being arrested and tortured in Turkey.