A Sri Lankan court on Thursday handed the death sentence to a soldier convicted of slitting the throats of eight Tamil civilians, including four children, during the island's separatist war.

Sergeant Sunil Ratnayake was ordered hanged over the massacre in 2000 of the ethnic minority Tamils who had returned to their bombed out homes on the northern Jaffna peninsula to try to salvage their belongings.

Ratnayake is said to have slit the throats of the eight, including the children, a five-year-old and three teenagers, before burying them in a mass grave, according to prosecutors.

The High Court in Colombo acquitted four other soldiers on Thursday over the killings, citing a lack of direct evidence, court officials said.

Army spokesman Jayanath Jayaweera said Ratnayake's sentence showed that the authorities were following due process in dealing with abuses committed during the war.

"This (verdict) is a good example to show the (justice) system is working well," Brigadier Jayaweera told reporters.

Soldiers are rarely tried in civilian courts in Sri Lanka. The military has faced international condemnation for alleged atrocities committed during the decades-long conflict that ended in 2009 when the military crushed Tamil rebels.

Sri Lanka has some 300 prisoners technically on death row, but there is an unofficial moratorium on capital punishment and authorities have not carried out an execution since 1976.

President Maithripala Sirisena came to power in January promising reconciliation and accountability for abuses during the war, including allegations that up to 40,000 civilians were killed in the final phase.

During the trial, prosecutors alleged the five soldiers had arrested the civilians in December 2000 in their village before carrying out the killings, some 400 kilometres (250 miles) north of Colombo.

One of the civilians survived the attack and raised the alarm, triggering a military investigation and the suspension of Ratnayake's entire unit of soldiers. Five were later indicted in 2003.