The Iraqi security forces on Saturday retook control of three towns in Salahudin province, while the troops buildup continues in south of the provincial capital city of Tikrit to attack it later, a provincial police source said.

The troops backed by the residents of the town of Ishaqi, some 90 km north of the capital Baghdad, fought back the extremists militant groups earlier in the morning and retook control of the town which was seized earlier by the militants, the source said on condition of anonymity.

Meanwhile, the security forces attacked the nearby town of al- Mu'tasim, some 100 km north of Baghdad, and seized the town after they defeated the militants, the source said.

Later Friday, the security forces backed by the residents of the town of Duluiyah, some 80 km north of Baghdad, retook control of their town after they clashed with a group of militants who fled the town, the source added.

Two more villages near the city of Baiji, some 200 km north of Baghdad, were also cleared from the militants by the residents and remnant of the local police who took up their arms and clashed with the gunmen, he said, adding that preparations are underway to retake the city of Baiji.

Since earlier in the day, the Iraqi army and police forces, backed by hundreds of volunteers who responded to a call by the country's most revered Shiite cleric, have gathered in Uwynat area, some 15 km south of Tikrit, which is about 170 km north of Baghdad, preparing for a major attack to retake the city, the source said.

He noted that Iraqi helicopter gunships continued their airstrikes on the posts of the militants around Tikrit.

The Sunni-dominated city of Tikrit, which is the hometown of former President Saddam Hussein, has been in the hands of the gunmen since Wednesday.

On Friday, the most influential Shiite cleric in Iraq Grand Ayatollah Ali al-Sistani called on Iraqis to take up arms to defend their country against insurgent groups who took control of large parts of the country.

"The situations in Iraq are very serious, entailing those who are able to volunteer to take up arms to defense their homeland," Sistani said in his order read on the weekly Friday prayers.

The security deterioration in Iraq started last week when bloody clashes broke out between the Iraqi security forces and hundreds of gunmen who took control of several neighborhoods in western part of Mosul and expanded later to others areas and provinces after the Iraqi security forces withdrew from the city.