Parliament in Germany is to debate secret plans to sell 200 tanks to Saudi Arabia despite a standing policy of not selling arms to repressive states.
News of the deal was leaked on Sunday by Spiegel magazine and confirmed by security sources in the Saudi capital, Riyadh.
German opposition parties are concerned that Saudi Arabia has been supporting a crackdown on unrest in Bahrain.
Germany's defence minister has refused to comment on the "classified" issue.
But opposition MPs say they will demand answers from the coalition government.
The BBC reports that it is believed that the Saudis wish to buy 200 Leopard II main battle tanks.
The Leopard II is used by Germany and many other NATO states.
Saudi Arabia already has about 1000 main battle tanks of US or French manufacture.
The kingdom's armour was visible in March when armoured cars were sent into neighbouring Bahrain, in a controversial move to back its rulers as they put down a popular uprising.
