The jihadists threw grenades and fired on the tribal Hashed forces stationed at Al-Radwaniyah, on the southern outskirts of the Iraqi capital, near the Baghdad airport.

"IS attacked the monitoring tower, killing five members of the tribal Hashed and six local people who had come to help repel the attack," a security source said.

A medic confirmed the toll to AFP, and said eight wounded were transferred to a hospital in central Baghdad.

There was no immediate claim of responsibility from IS.

IS swept across a third of Iraq in 2014, seizing major cities across the north and west and reaching the suburbs of the capital Baghdad.

After a fierce three-year fight backed by the US-led coalition, Iraq declared IS defeated in late 2017.

The coalition has significantly drawn down its troops this year, consolidating them to three main bases in Baghdad, Ain al-Asad in the west and Arbil in the north.

But IS's sleeper cells have continued to wage hit-and-run attacks on security forces and state infrastructure, particularly in desert areas where troops are stretched thin.

Attacks with such high tolls and so close to the capital have been rare, however.