KIRKUK, Iraq (AFP) - Islamic State group fighters executed nine people on Friday in two northern Iraqi towns on suspicion of ties to anti-militant Sunni grassroots organisations, security sources and witnesses said.

In the town of Az-Zab, 90km west of the oil hub of Kirkuk, six people were executed in public.

"IS executed four residents of the lower part of Az-Zab and two from villages near Az-Zwiya," a few miles further to the west, a local security official said.

Witnesses said the six were accused of being involved in efforts to organise Sunni resistance to IS in the Hawija region. They were executed on a marketplace, they said.

It was in the same area that residents of the village of Tel Ali burned an IS flag last month.

In retaliation, the militants abducted 50 residents and put up flags across the region, even booby-trapping some of them to stop locals from removing them.

In Baiji, about 35km to the south, three men were beheaded on Friday, a security official in the region said.

The official said the three men had been abducted a few days earlier and were former members of the Sahwa organisation funded by the US military to combat Al-Qaeda in 2007-08.

Iraq's Shi'ite-dominated government has been encouraging Sunni tribes to rise up against the extremist group that met little resistance when it swept through the country's Sunni heartland in June.

After targeting minorities in the areas they invaded, IS fighters have in recent weeks been killing many Sunnis they suspect of links with the government.

In Ishaqi, around 70km north of Baghdad, the bodies of six unidentified executed young men were found.

"Iraqi security forces found six bodies in Ishaqi canal. They had gunshot wounds to the head and chest," a senior police officer said.