The United States would invest $ 1 billion in Pakistans energy sector besides assisting the country in various hydel power projects, US Special Representative for Pakistan and Afghanistan Richard Holbrooke said on Tuesday. The top US envoy signed an accord in a ceremony at the Economic Affairs Division (EAD) to upgrade Tarbela Dam hydro-project. The dam is situated on the Indus River at a distance of about 70 kilometers North West of Rawalpindi/Islamabad and about 50 kilometers upstream of Attock.