US diplomatic cables newly released by Wikileaks are sharply critical of both the Sri Lankan government and the now defeated Tamil Tiger rebels.
The cables dating from 2007 suggest that the state colluded in paramilitary activities including killings, child trafficking and organised prostitution.
Meanwhile, the Tamil Tigers used systematic forced conscription during the war, which ended in 2009.
The cables are some of 2,000 released by whistle-blowing website Wikileaks.
Both the Tamil Tigers and Sri Lanka's government have long faced accusations by human rights groups of committing abuses during the 26-year conflict.
Other cables from early this year however said the state was improving its human rights record.
The cables, purportedly coming from the US embassy here, paint a bleak picture of northern and eastern Sri Lanka after the collapse of a ceasefire.
They quoted what they called "trusted embassy contacts" saying the Tamil Tigers were forcing one person per family to join their ranks.
They were also threatening families who did not bring their children back from jobs abroad in order to take up arms.
The cables also said that the government was supporting extra-judicial behaviour by pro-government Tamil paramilitaries, led by men who are now ministers.
Their sources said, for instance, that one paramilitary was believed to be trafficking boys as workers and girls as prostitutes.
One of the ministers concerned, however, has rejected all the allegations, telling the BBC Tamil Service: "We are not involved in trafficking or extortions."
Pro-government paramilitaries and the Tigers alike are accused in the cables of extorting money or food.
But a more recent cable from last January said Sri Lanka's government had "dramatically" improved its treatment of displaced Tamils and that the number of disappearances blamed on the state had significantly fallen.
The Sri Lankan government declined to comment on earlier Wikileaks cables.
The US embassy in Colombo stressed this month that cables reflected daily analysis and "candid assessments" and should not be seen as representing US policy.