ANKARA: Inmates in a prison in southeast Turkey set mattresses and blankets alight, starting a fire that killed 13 prisoners, authorities said Sunday.

Prime Minister Recep Tayyip Erdogan said the inmates set their bedding on fire following a fight that broke out inside a ward housing 18 prisoners late on Saturday.

Five of the inmates in the prison in the mostly-Kurdish and Arabic-speaking city of Sanliurfa were hospitalized but none was in serious condition.

The prisoners also barricaded the ward’s entrance using beds and other furnishings, hampering rescue efforts by guards, Justice Minister Sadullah Ergin told reporters after he and other ministers visited the prison in the city near the border with Syria. The five survivors escaped serious injury after shutting themselves in the ward’s bathroom, he said.

Inmates in Turkey have in the past set bedding alight in riots to protest poor prison conditions, but authorities insisted the incident was not a mutiny. There was no explanation however, as to what sparked the dispute in the ward. Ergin said an investigation had been launched and its results would be made public.

The fire, meanwhile, exposed the problem of overcrowding in some Turkish prisons. The Sanliurfa prison has a capacity of 600, but was holding some 1,000 prisoners, according to news reports. Ergin said the section where the fire broke out was designed to hold 12 inmates but was temporarily accommodating 18 convicts and jailed suspects still on trial.

“We have a capacity problem in Turkey’s prisons,” Ergin admitted, adding that the government was building 196 more prisons over the next few years to overcome shortfalls.

Authorities did not say whether the victims were burned or died of asphyxiation. Three guards suffered burns while trying to put out the blaze, while the prison director and eight other guards were treated for smoke inhalation, Ergin said.

The fire broke out in a section housing ordinary criminals and not terror suspects. A pro-Kurdish legislator, jailed for alleged links to an outlawed Kurdish rebel group, was not affected by the fire, the region’s governor, Celalettin Guvenc told reporters.

He said earlier that authorities had launched an investigation into the incident, including into possible delays by authorities or firefighters in responding to the fire.

“Why (the firefighters) weren’t there on time, what caused the fighting, why were these people killed? All of these will be investigated,” Guvenc said.

Erdogan said he would order an investigation into possible overcrowding. “I have been told by the governor that the ward’s capacity may not have been suitable to house 18 people,” he told reporters before his departure to Mexico to attend a Group of 20 summit.

Meanwhile, police used pepper gas to disperse families and protesters who attempted to make their way through a road block to reach the prison, the state-run Anadolu Agency reported.

The situation at the prison was calm on Sunday and Guvenc said prison authorities would grant increased visiting rights for families concerned about their loved ones.