Ingo Gaedechens, a member of conservative opposition party CDU and parliament's budget committee, said the tank deal is a manoeuvre by Pistorius to bypass the budget stalemate.

He told Reuters the tank order was justified but that the deal raised questions regarding future funding of German forces, as did the latest purchase of two frigates for more than 3 billion euros and the announcement of an order of Eurofighter jets for some 3 billion euros.

"There's one thing that all three projects have in common: The government refuses to answer the question how these purchases are meant to be bankrolled," Gaedechens said.

"The many blank cheques being issued by Chancellor Olaf Scholz and his Defence Minister Boris Pistorius cause an ever-growing financial bow wave - and nobody in the ruling coalition has any idea how to come to grips with this financial chaos," he said.