Germany on Saturday asked China to stop recruiting former Luftwaffe pilots to train its own air force, fearing they could reveal NATO secrets.

“I raised the question of Germany air force pilots who have apparently been recruited to train (Chinese) pilots,” Defense Minister Boris Pistorius told reporters.

He was speaking after meeting his Chinese counterpart Li Shangfu on the margins of a defense and security conference in Singapore.

“I indicated clearly that I expected this practice to cease immediately and told him he probably wouldn’t be very pleased either if I tried to do the same thing,” Pistorius added.

Li “didn’t deny it but downplayed its importance,” he continued, according to a ministry readout of his comments to the press.

German weekly Der Spiegel and public TV channel ZDF reported on Friday that several former air force pilots had been employed by China in recent years to train its own pilots.

Their salaries were apparently paid via shell companies in the Seychelles, the media said.

The matter is of deep concern to the parliamentary committee overseeing the German secret services, they reported.

“We are worried that military personnel who have previously worked for the German state could be in jobs that could lead them to betray state secrets,” the head of the parliamentary committee told ZDF.

The German pilots in question flew Eurofighter fighter jets and took part in NATO exercises.

Berlin fears that secrets concerning interventions and tactics used by the transatlantic military alliance could be revealed to the Chinese.

ZDF said the defense ministry planned to launch an inquiry.

Similar cases have surfaced in Britain and the United States in recent years.

They come at a time of heightened tensions between China and neighboring Taiwan.

China claims self-ruled democratic Taiwan as its territory, and has vowed to take it one day — by force if necessary.