The uprising against extremists in Anbar province, where radicals from the Islamic State of Iraq and the Levant (ISIL) group and insurgent allies hold major areas, came a day after Nouri al-Maliki, the Iraqi premier, abandoned his bid for a third term.
The current effort could potentially be a major turning point in Iraq's two-month conflict against an ISIL-led offensive.
"This popular revolution was agreed on with all the tribes that want to fight ISIL, which spilled our blood," Sheikh Abdel-Jabbar Abu Risha, one of the leaders of the uprising, told AFP.
ISIL-led insurgents launched a major offensive in June that swept security forces aside and overran large areas of five provinces, including Anbar, where parts of provincial capital Ramadi and all of the city of Fallujah had already been outside government control since January.
Anbar police chief Maj. Gen. Ahmed Saddak said security forces were backing the uprising, which began at 6:00 am Friday.
"The battles are continuing until this moment," he said, putting the toll at 12 militants killed and adding: "We will not stop until the liberation of Anbar."
The push by tribesmen and security forces began with attacks on multiple areas northwest of Anbar provincial capital Ramadi, Abu Risha and Saddak said.
Police Col. Ahmed Shufir, meanwhile, said that Kataeb Hamza, a group that fought against Al-Qaeda-linked militants in past years, has been reformed and is based out of the town of Haditha in Anbar province.
Its forces aim to fight against militants who hold areas west of the town, he said.
Abu Risha said that the effort had been in the works for weeks and was not linked to Maliki's announcement Thursday night that he would step aside.
Shia volunteer fighters have already started forming battalions to protect Iraqi towns against ISIL radicals who are reported to be largely funded by foreign countries.
ISIL overran Iraq's second largest city, Mosul, in June. They had taken the central city of Fallujah and parts of nearby Ramadi in December 2013.
SHI/SHI