Troops backed by helicopters were searching for Izzat Ibrahim al-Douri, head of Saddam's now-outlawed Baath party, in villages around the former ruler's hometown of Tikrit, 150 kilometers (95 miles) north of Baghdad.

Capturing the most prominent Baath leader would be a major victory for the Shiite Prime Minister Nouri al-Maliki before provincial elections that will measure his political muscle for the 2014 parliamentary ballot.

"We have solid information that he is in Dour since last night, now we have closed the area, announced a curfew and are searching house by house," said one senior security officer involved in the operation.

Douri was long believed to be living outside Iraq, and he was last seen in January in a video message encouraging Sunni Muslim protesters to resist Maliki's government.

Maliki is facing huge Sunni rallies in western Iraq protesting against what they see as the marginalisation of their minority sect since 2003. Many Sunnis feel they have been unfairly targeted for arrest by security forces.

The Shiite leader has offered some concessions to protesters, especially in the so-called de-Baathification law — meant to keep former Baath party members out of government posts — and Iraq's tough anti-terrorism laws.

Maliki is also under pressure from other Shiite parties in his coalition, who are trying to use his concessions to Sunnis for political gain in the local elections on Saturday for provincial council members.

Douri was vice-chairman of Saddam's ruling Revolutionary Command Council until the invasion. He also headed the Army of the Men of the Naqshbandi Order or the Naqshbandi Army formed after 2007 to fight U.S troops.

BOMBINGS

Sunni Islamist insurgents and al-Qaida still carry out coordinated attacks like the string of bombings on Monday that killed 30 people in Baghdad and other cities.

Security officers involved in the Douri operation said they believed he moved between Tikrit and the towns of Dour and Hawija. One security source said Douri visited Sunni demonstrators in Tikrit before he went to Dour where he has many supporters and owns a villa.

"The special forces early this morning raided the villa of his excellency. They searched it, but found nothing," said Dhiyaa Ibrahim, one of Douri's neighbors.

Ibrahim said the troops searched other houses and nearby villages and arrested four people.

In January's video, Douri, surrounded by men in uniform, urged Sunni nationalists to resist the Shi'ite government, which has edged closer to Iraq's non-Arab Shiite neighbor Tehran since the invasion and fall of Sunni strongman Saddam.

Since the last American troops left, Baghdad's national government has been deadlocked by tensions among Shiite, Sunni, and ethnic Kurdish parties who split government posts among them in an unwieldy power-sharing arrangement.

After the invasion, Douri was ranked sixth on the U.S. military's list of 55 most wanted Iraqis and a $10 million reward was offered for his capture. U.S. officials said he had organized a Sunni insurgency against American troops.