Up to 40 people were killed and 100 others wounded when gunmen stormed into the provincial council of Salahudin province on Tuesday and held hostages in the building, including council members, a provincial police source told Xinhua.

"Our latest reports said that 40 people were killed and some 100 others wounded by the attack," the source said, citing reports collected from Tikrit's hospitals.

"Most of the victims were security members and employees of the provincial council, four of the killed were provincial council members," the source said.

Earlier the source put the toll at 12 killed and 60 wounded by the coordinated attack.

The attack took place after midday when about 10 gunmen in police uniforms, wearing explosive belts stormed into the building of the provincial council in central Tikrit, some 170 km north of Baghdad, and fierce clashes erupted between the attackers and the guards of the compound, the source said.

The gunmen started their attack immediately after they blew up a booby-trapped car outside the building which was also hit by two mortar rounds, he said.

Iraqi security force are surrounding the building and special police forces have entered the building and engaged with the gunmen, who were holding undetermined number of hostages in the second floor, the source added.

U.S. helicopters flew over the area as U.S. and Iraqi SWAT ( Special Weapons And Tactics) force arrived in the afternoon at the scene and started operation to free the hostages and killed the suicide bombers, the source said.

Brigadier General Imad Nofan, the provincial police chief, was among the deaths, and Ahmed Shindah, provincial deputy governor for security affairs and five of his bodyguards, were among the wounded, the source said.

Three more police officers were also killed by the attack, the source added.

Among the dead was the journalist Sabah al-Bazi, a correspondent for al-Arabiyah satellite channel and for the CNN, in addition to a cameraman for the Iraqi television of al-Fayhaa, the source said.

An witness who was at a meeting, held by the head of the provincial council, in the building, told Xinhua by telephone that "the attackers immediately entered the building after a powerful explosion outside the building and started shooting inside the building's rooms and on every body they see on their way."

"Two suicide bombers blew themselves up at the beginning of the attack inside the building," he said.

"I myself jumped from the second floor to the garden of the building and creep outside the building," said the witness who refused to be named because he is not authorized to speak to the media.

"Before I ran away from the building, I saw the head of the provincial council fleeing the building from the emergency gate at the rare of the building," he said.

Authorities in the city blocked the entrances of Tikrit and imposed curfew in the city, where the streets were deserted and only military vehicles and ambulances could be seen moving, the source added.

Salahudin province, located in northern central of Iraq, is mainly Sunni province. Its capital city of Tikrit is the hometown of former President Saddam Hussien.