The US sponsored a resolution in the UN Human Rights Council which called for an external probe in Sri Lanka's civil war which ended in 2009 and an improvement to human rights.
"…[W]e are not at this point discussing sanctions. We are very much committed to seeing progress on those issues that were raised at the Human Rights Council," Ambassador Michele J Sison told foreign correspondents in Colombo.
"So we and others in the international community will continue to monitor and speak out when these issues of concern - actions against human rights defenders, attacks against religious minorities and journalists and others."
The UN resolution did not close the door to a domestic mechanism, she said.
She said all alleged attacks on journalists, human rights defenders and members of religious minorities should be investigated.
"Additionally, we echo the High Commissioner’s concerns regarding the increase of sexual harassment and violence against women in the former conflict zones," she said.
"The resolution urges the Government to hold perpetrators of such attacks to account and to take steps to prevent such attacks in the future.
"Impunity is contagious, and there has been an alarming surge in attacks against members of religious minorities in Sri Lanka."
She said on March 09, a pastor in a Church in Badulla district was assaulted by a mob while a service was in progress. On March 26, two petrol bombs were thrown at a mosque in Dambulla.
"I also note our serious concern about reprisals against those who meet with visiting diplomats and UN officials, or those who traveled to Geneva to meet with various delegations during the month of March," she said.
"It is disturbing to see this targeting of human rights defenders who have devoted their careers and lives to promoting and defending the rights of their fellow Sri Lankan citizens."
Ambassador Sison said the UN resolution was not against Sri Lanka and the US relations relationship with Sri Lanka, Sri Lankan people including businessmen, academics and civil society activists was "broad" and "deep".
The American Chamber of Commerce was active in Sri Lanka and the US was a key trading partner, she said.
Trade promotion, expanding market access, intellectual property rights and technical co-operation was being expanded in discussions under a Trade and Investment Framework Agreement (TIFA) signed in 2002, she said.
A mission from the Overseas Private Investment Corporation, a state agency, was visiting Sri Lanka this week.