At least 700 Taliban fighters have crossed from Pakistan into Afghanistan to reinforce guerrillas attacking a key dam, a major source of electricity and irrigation, a provincial governor said on Monday. “We have got confirmed reports that they are Pakistani, Uzbek and Chechen nationals and have sneaked in,” Helmand Governor Asadullah Wafa told Reuters by telephone. The Kajaki dam has seen major fighting in recent weeks between the Taliban and NATO forces, mainly British and Dutch. NATO-led troops have been conducting operations in the area for several months to allow reconstruction on the dam and the power transmission lines to boost output, after fighting halted refurbishment last year. A spokesman for the NATO-led force confirmed rebel movements in the dam area, including across the border, but could not confirm the governor’s numbers or any other details. Built by the Soviets in 1953, the dam irrigates about 285,000 acres of farmland and two hydroelectric plants built by the United States in 1975 have a capacity of 33 megawatts. A third plant is planned, which would almost double that capacity by 2009. Wafa said the Taliban fighters were brought in by local commanders for a joint operation with Al Qaeda. “They are planning to destroy the Kajaki dam,” he said, accusing Pakistan’s military intelligence agency, ISI, of providing training and logistical support for the guerrillas. “Pakistan is supporting the Taliban in order for them to keep fighting on in Afghanistan. They don’t want Afghanistan’s development and reconstruction,” he said. Pakistan denies continuing to support the Taliban.