Excavators have unearthed several skeletons from what seems to be a mass grave in Sri Lanka, shedding light once more on the country’s human rights record during its bloodiest insurgencies.

Several skeletons, or parts of skeletons, belonging to 59 people were found at a building site near a hospital in Matale, 142km (88 miles) from the capital of Colombo.

Authorities said it is possible the remains are those of the forgotten victims of the violent insurgencies in the early 1970s which killed more than 150,000 people but they have not ruled out them having died of natural causes many years ago.

“We can’t exactly say when they have been buried. These could be missing people,” says Ajith Jayasena, the judicial medical officer at the hospital near the site, referring to the victims of political violence.

Sri Lanka is under pressure from the United Nations to address human rights problems and the deaths of thousands of civilians as the three-decade war with Tamil rebels drew to a close in 2009. The government has long been criticized by human rights organizations for failing to properly investigate alleged war crimes. Sri Lanka has denied all accusations of human rights violations, Reuters reports.