China may secretly have supplied Pakistan with chemical components for a newly opened nuclear reactor - breaking its commitments to the US. In testimony to a congressional committee, Nuclear Control Institute president Paul Leventhal said the recent opening of the plutonium-processing plant at Khushab might have partly prompted the Indian tests. Mr Leventhal said Beijing had supplied heavy water to a civilian reactor in Kanupp, Pakistan. But during talks with the United States Government before October's signing of the Sino-US nuclear co-operation agreement, Beijing promised Washington it would not sell Islamabad heavy water for the plant at Khushab, which is a military facility, he told the House of Representatives commerce sub-committee on trade. However, he said evidence had emerged that China had over-supplied Pakistan with heavy water for the civilian plant - leading to strong suspicions that the remaining amount had been diverted to Khushab. Mr Leventhal said: 'If China knowingly oversupplied Pakistan with heavy water and the heavy water was diverted by Pakistan to produce military plutonium, this, in our view, would constitute indirect assistance by China to Pakistan's nuclear weapons programme - something President Bill Clinton certified to Congress that China had assured him would not happen. 'The start-up of the Khushab reactor is extremely significant. It provides Pakistan with the capacity to produce one or two bombs worth of plutonium a year.' Mr Leventhal said the issue was extremely worrying, coming on the heels of another revelation that state-controlled mainland companies had been detected by US intelligence negotiating to sell a chemical component for uranium enrichment to Iran.