WASHINGTON, July 1 (Reuters) - The U.S. government voiced concern on Wednesday over actions taken by Niger's President Mamadou Tandja to extend his rule in the West African country. "These decisions undermine Niger's efforts over the last ten years to advance good governance and the rule of law," White House spokesman Robert Gibbs said in a statement. Tandja responded to the rejection by Niger's highest court of his plan to seek at least another three years in power by sacking the judges and naming a new Cabinet. ....U.S. concern about the situation in Niger comes at a time when Washington...