Neither IED nor mortar. EOD discharge of explosives seized during the training operation.
Short summup of training situation: A patrol discovers multiple hostiles setting up a rocket launcher close to the camp, QRF is called to attack that bunch. After the battle, EOD discharges rocket launcher and ammunitions.
Good clip about some German paratroopers patrolling in Northern Afghanistan.
Some interesting scenes are in it. Outright does the patrol commander admit that they rather do not want to describe what happened during attacks against them...