Gunmen have seized control of a prison in the Iraqi city of Tikrit after clashes with guards that left at least two dead, a deputy governor and security officials say.

"The attackers are controlling all the (entrances and exits) and the observation towers, and ... security forces are surrounding the prison," Salaheddin provincial deputy governor Ahmed Abdul Jabbar Abdul Karim told AFP news agency.

A police officer put the toll from attack at four police and two gunmen killed.

Tikrit, located 160 kilometres north of Baghdad, is the ancestral home of former leader Saddam Hussein.

Accounts diverged as to whether the unrest began with an outside assault, a riot inside the prison, or possibly both.

A traffic police lieutenant colonel located near the prison said armed men blew up a portion of the prison fence, and that between 30 and 40 prisoners were able to escape.

Other witnesses said the prisoners were able to seize the guards' weapons, and that more than 100 of them escaped.

Al-Qaeda's front group the Islamic State of Iraq said in July that it was launching a "new military campaign aimed at recovering territory".

An earlier message posted on jihadist forums said the ISI would begin targeting judges and prosecutors, and try to help its prisoners break out of jails.

While insurgents opposed to the Baghdad government are regarded as weaker than in past years, they have shown they can strike at even the most highly secure sites in Iraq.