The German intelligence service (BND) considers the security situation to be critical, expecting an increase in attacks against Western soldiers, according to the report entitled "Afghanistan until 2014 a forecast."

Following the planned withdrawal of Western combat troops in 2014, up to 35,000 foreign soldiers will be necessary, mostly to train the Afghan army, the BND analysis said.

They will need to be combat troops to provide force protection and in some cases, they will have to be special operations forces to fight terrorism, it said.

With nearly 4,800 soldiers, Germany is the third largest force under NATO's International Security Assistance Force, behind Britain's 9,500 troops and the more than 90,000 US troops.

German intelligence also sharply criticised the government of Afghan President Hamid Karzai, Der Spiegel said. "The tendency towards corruption, nepotism and influence-peddling by certain people will continue," the BND predicted.

Over 50 NATO troops have been killed this year in so-called insider attacks by their Afghan allies.