"The troop withdrawal from Iraq will make it a fertile ground for terrorism and attacks will hit the region and Europe," he said at a press conference with his Jordanian counterpart Ayman Safadi in Amman.
Iraq has been roiled by protests since October against deep-seated corruption and living condition amid calls for the withdrawal of U.S. forces from the country.
As for tensions between the U.S. and Iran, Maas said, "If Iran wants to de-escalate, then it must stop agitation in its region, which also applies to Iraq".
Tension soared earlier this month after the U.S. assassinated Iranian general Qasem Soleimani in a drone attack in Iraq. Tehran retaliated with firing a dozen ballistic missiles at Iraqi airbases housing U.S. troops.
Reporter's code: 50101