Animal Planet's previous most-watched telecast, 2005's "Dragons: A Fantasy Made Real," scored 2.8 million total viewers.

The exercise will "test new types of combat forces including units using digital technology amid efforts to adjust to informationalized war".

The police chief of Kandahar district said that the two attackers were former policemen who had rejoined the force only two days previously.

The spacecraft is carrying Russian cosmonaut Fyodor Yurchikhin, and astronauts Karen Nyberg of NASA and Luca Parmitano of European Space Agency.

Obama recently indicated he was scaling back the drone strike programme, winning cautious approval from Pakistan.