ANKARA, Turkey - 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 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 that 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.

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.

Erdogan said he would order an investigation into possible overcrowding.

The situation at the prison was calm on Sunday.