"We are concerned about the reports we receive ... the United States takes these issues very seriously," he said.
"Human rights were an important part of a dialogue I had with President Rajapakse. We emphasised for a strong human rights performance on the part of the government and all of its branches," Mann added.
The remarks followed a State Department report this week highlighting Sri Lanka's deteriorating human rights situation.
During his two-day visit, Mann discussed the peace process, human rights and access to conflict areas with the president, government ministers, civil society leaders and charities, the US embassy here said.
International human rights organisations have said rights abuses are on the rise as conflict escalates between security forces and separatist Tamil Tiger guerri