NATO’s secretary-general apologized to Turkey on Friday over military exercises in Norway during which Turkey’s founding leader, Mustafa Kemal Ataturk, and the 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 criticized the alliance.

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

Details of the incident were sketchy. Erdogan said Ataturk’s picture and his own name were featured on an ‘enemy chart’ during the drills.

The individual who posted the material was described as a Norwegian civil contractor seconded by Norway, and not a NATO employee.

NATO Secretary-General Jens Stoltenberg issued a statement saying: ‘I apologize for the offense caused.’ He said the incident was the result of an ‘individual’s actions’ and didn’t reflect the views of the alliance.

He added that the individual was removed from the exercise and an investigation was underway.

‘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.’

Stoltenberg apologized again at the Halifax International Security Forum in Canada. He said he’s already spoken with the Turkish defence chief and that it ‘won’t create any lasting problems, and I think it’s already behind us.’

Norwegian Defense Minister Frank Bakke-Jensen apologized for the incident as well.

‘The message does not reflect Norway’s views or policies and I apologize for the content of the message,’ Bakke-Jensen said in a statement. He added that ‘Turkey is an important ally in NATO, and we value our good cooperation.’

The Joint Warfare Centre is a multi-national NATO unit based in Stavanger, 300 kilometers (186 miles) 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.