In the town of Az-Zab, 90 kilometres (55 miles) 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.
In retaliation, the jihadists 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 35 kilometres (20 miles) to the south, three men were beheaded today, 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 Shiite-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.
