KERBALA, Iraq (Reuters) - Hundreds of thousands of pilgrims poured into Iraq's holy city of Kerbala on Saturday for a rite that has become an annual show of strength for the Shi'ite majority, defying bomb attacks across the country.

Many of the pilgrims have walked for days in temperatures of up to 50 degrees Celsius (122 Fahrenheit) to mark the birth of Imam al-Mehdi, a Messiah-like figure Shi'ites believe vanished centuries ago and will return to bring peace on earth.

A bomb in a parked car struck pilgrims walking in Baghdad early on Saturday, killing six and wounding 10, police said.

On Thursday, a female suicide bomber killed 19 pilgrims and wounded 75 when she blew herself up amid a group making the journey on foot near Iskandariya south of Baghdad.

Authorities said they had managed to avoid bloodshed in Kerbala itself after last year's pilgrimage was marked by gun battles between Shi'ite factions and Iraqi security forces.

"Thank God the situation is under control. We haven't observed any security violations. People are happy and cooperating with security forces," said Captain Abdullah Muhammad of the Iraqi army in Kerbala.

"This year we haven't seen the pilgrims holding pictures of clerics or shouting against the government like last year."

Pilgrim Najim Muhammad al-Lami, 43, said he had walked for six days with his wife and two children from the southern city of Basra.

"We come every year. Last year my son was wounded by a bullet during the pilgrimage, but I insisted on coming again anyway. This year the situation is more secure and organized."

DEMONSTRATIONS OF STRENGTH

Several of Iraq's annual pilgrimages have evolved into massive demonstrations of strength for the Shi'ite majority since the fall of dictator Saddam Hussein, a Sunni Arab who restricted Shi'ite religious practice.

The events are targets of attacks despite declining rates of violence in the country.

Iraqi security forces, backed by helicopters and hundreds of snipers on rooftops, say they will search pilgrims and use sniffer dogs to help find explosives. U.S. forces have had virtually no troops stationed in the vicinity for some time.

Authorities have banned people from carrying weapons and chanting sectarian slogans.

Police in fatigues and red berets checked identity cards and searched the faithful entering the golden-domed Imam Hussein mosque, strung with brightly colored lights. Nearby, makeshift clinics were set up in tents. Some pilgrims donated blood.

Many of the worst attacks of Iraq's war have taken place during pilgrimages. Bombs killed 171 people during a pilgrimage in 2004, heralding Iraq's looming sectarian conflict.

Rumors of a bomb on a Baghdad bridge during a pilgrimage in 2005 caused a stampede in which more than 1,000 people died, the deadliest incident of the war. During the last major pilgrimage in July, three female suicide bombers killed nearly 30 people.

Outrage after the violence among Shi'ite groups at last year's pilgrimage prompted anti-American cleric Moqtada al-Sadr to declare a ceasefire of his Mehdi Army militia, which U.S. forces say has helped contribute to a reduction of violence.

Last week Sadr formed a new social wing of his movement and said most Mehdi Army fighters would disarm. The militia would begin disbanding if U.S. forces withdraw on a timetable.