DAR ES SALAAM, Aug 4 (Reuters) - A senior U.S. government official expressed concern on Wednesday over the arrest and imprisonment of Tanzania’s opposition leader Freeman Mbowe who was charged with terrorism-related crimes in late July. Mbowe, chairman of the leading opposition party CHADEMA, was detained in the city of Mwanza on July 21 as he was preparing for a meeting to discuss proposals for a new constitution. “We have expressed our concern about the treatment and imprisonment of the opposition leader Mbowe," Victoria Nuland, Under Secretary for Political Affairs, told reporters. Nuland, on a tour of several African countries, was speaking at the end of a visit to Tanzania during which she met President Samia Suluhu Hassan and her foreign minister as well as opposition leaders. CHADEMA said the imprisonment of its leader was proof that Hassan was persisting with the authoritarianism of her late predecessor John Magufuli. The government denies that accusation. Inspector General of Police Simon Sirro told reporters on Monday to allow the courts to judge Mbowe. "Let them wait for the court to decide," he said.