HONG KONG, July 1 (Reuters) - Hong Kong"s national security law imposed on the city a year ago guarantees human rights, including freedom of the media and assembly, the city"s No. 2 official John Lee said on Thursday. Lee, acting Chief Executive while leader Carrie Lam is in Beijing, was speaking at a flag-raising ceremony marking the 24th anniversary of the former British colony"s return to Chinese rule in 1997, which coincides with the centenary of the Chinese Communist Party.