Indonesia must step up efforts to investigate serious human rights abuses surrounding the eruption of a "mud volcano" which displaced 36,000 people, the national human rights commission said Wednesday.

The commission investigator said the state body had found "serious" rights violations relating to the disaster and called on the government to punish those responsible.

"A serious human rights violation has occurred," Kabul Supriyadhie told a forum of activists and journalists.

The mud volcano, dubbed "Lusi", erupted from a well being dug by Lapindo Brantas, an oil and gas company owned by billionaire welfare minister Aburizal Bakrie, in East Java two years ago on Thursday.

Thirteen people were killed in the initial eruption and 12 villages were inundated as the stinking, methane-filled mud spewed across 640 hectares (1,580 acres) of surrounding countryside, forcing thousands to flee their homes.

Lapindo blamed an earlier earthquake and a court has ruled that the eruption was a natural disaster, but independent researchers say the volcano was almost certainly woken by the drilling.

"This is a problem that we deem serious, where the state has failed to protect and guarantee basic rights of the victims of the incident and has no political will to pressure PT Lapindo Brantas to take their responsibility," Supriyadhie said.

He said the company had no legal authority to drill in the densely populated area and local residents had not been informed of its operations.

The rights commission also found it puzzling that the government had not investigated the explosion that killed the 13 company workers at the site.

"No legal process had been launched in relation to the incident. The police said it cannot be investigated because the pipe (that exploded) is now gone and buried under the mud," he said.

Meanwhile, Indonesian police are pursuing a criminal case where Lapindo executives are among 13 named as suspects over the drilling mishap that caused the mudflow.

The original police file on the case was submitted shortly after the mud began flowing, but the case has seen long delays.

"There was a prolonged debate whether the phenomenon was a natural disaster or man-made. This should be decided in court by a judge, not during investigation," said Supriyadhie.

Separate Jakarta courts in November and December last year rejected two lawsuits brought by environmentalists against Lapindo and the government for neglecting to prevent the mud volcano from causing a humanitarian disaster.

The commission, formed by presidential decree in 1993, has been widely criticised for its failure to push the government to investigate rights abuses.