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JAKARTA (Reuters) - Indonesia has launched an investigation into accusations of mistreatment by prison guards, after around 350 inmates broke out of an overcrowded jail on Sumatra island in Riau Province last week, an official said on Monday.

Three days after the mass escape, 151 prisoners were still on the run and 197 have been recaptured, Ferdinand Siagian, the head of Riau Province’s Law Ministry office, which oversees Pekanbaru prison, told Reuters.

“We are carrying out a deep investigation into the serving officers,” said Siagian, adding that the warden of the prison had been transferred to a different post.

Before the prison break, prisoners had complained about mistreatment, accusing some guards of violence, Siagian told Metro TV on Friday.

Family members of Pekanbaru inmates also said guards had extorted money from prisoners and their families to ensure they had sleeping space or to speed up visits, according to media.

The Pekanbaru prison housed about 1,800 prisoners, but was only meant to hold up to 700 inmates, a Riau police spokesman said.

To address overcrowding, Siagian said Riau’s Law Ministry office was building a new prison to house drug-related inmates.

Indonesia’s war on narcotics has led to a spike in the number of convicted drug offenders, stretching an already overwhelmed prison system.