BAGHDAD (AP) _ Black-clad men flagellating themselves with chains in grief at the martyrdom of a revered Shiite Muslim figure marched Tuesday through the city of Karbala as a pilgrimage marred by deadly attacks neared its conclusion.

In northern Iraq, a suicide bomber attacked a bus outside the city of Mosul. The Iraqi army said nine were killed and nine injured but the U.S. military put the toll at eight dead and eight injured. The two accounts could not immediately be reconciled.

Shiites from all over Iraq have walked to the holy city of Karbala, 50 miles south of Baghdad, to commemorate the end the mourning period following the anniversary of the death of Imam Hussein, who was slain in a seventh century battle. He is buried in Karbala.

Major Shiite events have frequently been targeted in the past by suspected Sunni insurgents in their drive to stoke sectarian violence. However, recent commemorations, including the Ashoura festival in mid-January, have passed without major bloodshed amid an overall decline in violence across Iraq.

Overall, February already has seen a rise in Iraqi casualties to at least 670, up from 609 in January, which had the lowest monthly death toll in more than two years.

In Karbala, Associated Press Television News footage showed processions of men, some barefoot, marching in time and flagellating themselves to the beat of a drum. Crowds of black-robed women five or six deep watched from the side and tapped themselves over the heart also in time with the drum.

Iraqi soldiers patrolled the streets, and an Iraqi Army armored vehicle kept watch from a position fortified by blast walls and sandbags.

Police Chief Raid Shakir Jawdat has said 40,000 police officers and military troops are being deployed to prevent attacks, with patrols on the outskirts of the city guarding against rocket or mortar attacks and hundreds of snipers on tall buildings.

Iraqi and U.S. authorities have said at least 8 million pilgrims are expected to swell the streets of the city by the time the time ceremonies reach their peak on Wednesday and Thursday. With heavy security in Karbala, extremists have struck in recent days at those on their way. At least 63 pilgrims have been killed.

The United States blamed Sunni-led al-Qaida in Iraq on Monday for the sectarian attacks, the worst of which killed 56 and wounded scores of pilgrims who were taking a break from their travels Sunday at a refreshment tent.

In Mosul, the attack targeted a bus loaded with about 45 passengers heading for Syria from Mosul when the explosion went off about 40 miles west of the city, said an army officer, who spoke on condition of anonymity because he wasn’t authorized to release the information.

According to a preliminary report, the army said that the suicide bomber ordered the bus driver to take a route away from the highway to dodge army check points. When the driver refused, the bomber blew himself up when the bus was about 500 yards from an army check point.

However, the U.S. military gave a different account. It said the attack occurred at a routine checkpoint where the Iraqi Army was searching passengers for their identity cards. After the bomber exited the bus, he detonated a suicide vest, the military said.

Mosul has been billed by the U.S. military as the last major urban stronghold of al-Qaida in Iraq and is a major focus of combined U.S.-Iraqi efforts to drive out extremists whose influence has already been slashed in Baghdad.

In other violence, police said gunmen in civilian clothes stopped two buses at a fake checkpoint on a highway in volatile Diyala province and kidnapped 21 men. They later released three women. The area is rife with al-Qaida insurgents and police said the bus was headed to Baqouba from northern Kirkuk.

Fifteen gunmen broke into a house in the village of Tuz Khormato, 130 miles north of Baghdad, killing an Iraqi soldier and wounding his brother.

In Hawija, 150 miles north of Baghdad, two members of the local awakening council – Sunni fighters who have turned against al-Qaida – were killed after gunmen opened fire on a checkpoint.

In each case, police officials spoke on condition of anonymity because they were not authorized to release the informatio