Six guards and 30 detainees were killed in a prison break north of the Iraqi capital during which 40 inmates escaped, an interior ministry spokesman said Saturday.

The spokesman said the break on Friday started when an inmate grabbed a weapon from a warden at the prison on the main police compound in Khalis, a town around 50 kilometres (30 miles) from Baghdad.

"One of the prisoners seized a weapon from a guard. After killing him, the inmate headed up to the weapons storage and he seized more weapons," Brigadier General Saad Maan told AFP.

"Clashes erupted inside. We lost a first lieutenant and five policemen, forty prisoners fled. Nine of them were held on terror charges and the rest for common crimes," he said.

Maan added that 30 prisoners who had been held on terrorism charges were killed in the clashes.

Iraq has been plagued by several prison breaks over the past two years, including in the early days of the huge June 2014 offensive by the Islamic State jihadist group.

The jihadists freed and recruited hundreds of Sunni inmates, including in the cities of Tikrit and Mosul.

A mass break-out at the Abu Ghraib prison west of Baghdad during which more than 500 inmates, including top Islamist militants, escaped in July 2013 is considered to be one of the key moments in the rise of IS.

At least 11 people were killed on Friday in a double suicide attack claimed by IS against a Shiite mosque in Baladruz, east of Khalis in Diyala province, northeast of the capital.

Government and allied forces clawing back territory from the jihadists announced earlier this year that Diyala had been completely liberated but sporadic attacks have continued.