The United States has warned that Sri Lanka could face a return to conflict unless it probes war crimes allegedly committed by its troops and addresses the grievances of its minority Tamil population.
Ambassador Michele Sison said Monday night that "important steps in achieving real reconciliation" had not even begun since Colombo declared an end to decades of separatist war in May 2009.
"History has shown that societies that do not adequately address reconciliation and accountability usually return to a conflict situation at some point down the road," Sison told a meeting of the Foreign Correspondents' Association in Colombo.
"However difficult this process is, it is ultimately vital to the stability of Sri Lanka," she added.
The UN Human Rights Council condemned Sri Lanka last month for failing to investigate alleged war crimes in the final battle against Tamil Tiger separatists.
Sison said Washington was working to build international consensus on further unspecified action against Colombo, either within the UN Human Rights Council or outside.
Rights groups have called for tougher action, including sanctions. They say up to 40,000 civilians were killed in the final months of fighting in 2009, a charge Sri Lanka denies.
Sison said Washington was concerned that repeated international calls to improve Sri Lanka's human rights record had not been heeded.
Attacks on independent media and journalists continued unabated, she said, while also raising concerns over the judiciary. Sri Lanka sacked the chief justice earlier this year, drawing further international condemnation.