The United States said on Friday it was disturbed by reports that five Hong Kong booksellers critical of China's leaders had disappeared. Lee Bo, 65, a shareholder of Causeway Bay Books and a British passport holder, went missing from Hong Kong last week, though his wife has said he voluntarily traveled to China and has withdrawn a missing person report. Four other associates of the publisher that specializes in selling gossipy political books on China's Communist Party leaders have been unaccounted for since late last year.