A German military helicopter which crashed in Afghanistan last month, killing all seven soldiers on board, probably went down because it had been incorrectly reassembled after it was shipped from Germany, Defense Minister Peter Struck said Wednesday.

Like other helicopters used by German peacekeepers in Afghanistan, the Sikorsky CH-53 which crashed near Kabul Dec. 21 as it returned from a routine patrol had been partly dismantled before it was sent to Afghanistan.

"The cause is neither an enemy attack nor a mistake by the crew," Struck said on ZDF television, citing first results of an investigation by his ministry. "It lies in human error, apparently with the soldiers who reassembled the helicopter."

Parts of the drive system in the helicopter were "incorrectly screwed together," the ministry said, promising generous financial support for the victim's families.

The crash was the worst for German troops since Berlin began taking part in international peacekeeping missions. The seven German soldiers killed were among the 4,800 peacekeepers who have been in Afghanistan for a year to try to establish security.

German lawmakers voted in November to double the number of German peacekeepers in Afghanistan to 2,500.