Three female suicide bombers killed 28 people and wounded 92 when they blew themselves up among Shi'ites walking through the streets of Baghdad on a religious pilgrimage on Monday, Iraqi police said.

In the northern oil city of Kirkuk a suicide bomber killed 22 people and wounded 150 at a protest against a disputed local elections law, Iraqi health and security officials said.

The attacks mark one of the bloodiest days in Iraq in months and underscored the fragility of recent security gains in the country, where violence is at its lowest level since early 2004.

There was no immediate claim of responsibility for the Baghdad blasts but Sunni Islamist al Qaeda often targets Shi'ite pilgrims. It considers Shi'ism - the majority Muslim denomination in Iraq - heretical.

"These blasts that happened today will increase our determination to finalise this ceremony . and defeat terrorism," pilgrim Taher Abd-Noor said.

At least 1 million people are expected to take part in the pilgrimage in the Iraqi capital, which peaks on Tuesday and marks the death of one of Shi'ite Islam's 12 imams, one of the most important events in the Shi'ite religious calendar.

Prime Minister Nuri al-Maliki has urged foreign dignitaries and firms to come to Iraq, citing stronger Iraqi security forces more able to keep the peace with less U.S. military help.

The apparently coordinated blasts in Baghdad shattered a period of relative calm in the city and took place despite heavy security for the annual pilgrimage to the Kadhamiya shrine.

CARNAGE

The U.S. military said it was possible three suicide bombers had carried out the attacks in the capital but did not specify if they were women. It put the death toll at 20.

Al Qaeda has increasingly used women to carry out suicide attacks because they can often evade the more stringent security checks applied to men. Women have carried out more than 20 suicide attacks in Iraq this year.

Reuters television pictures showed police, firemen and other workers washing blood and clearing debris from the street at the scene of one of the blasts in Baghdad. A Reuters witness saw workers collecting pieces of flesh and body parts.

The blasts occurred in central Baghdad, an area many pilgrims pass through on their way to the shrine.

Police on Sunday also said gunmen killed seven pilgrims in southern Baghdad as they made their way to the shrine, but some officials on Monday questioned this account, saying they were not aware of the incident.

In Kirkuk, Kurdish television footage showed thousands of people demonstrating against Iraq's provincial elections law when an explosion prompted a rush for cover. A Reuters witness said there was a stampede as police fired into the air.

Tensions have been in high in the disputed oil-rich city before provincial elections expected to take place either late this year or early in 2009.

"The death toll so far is 22 killed and more than 150 wounded," said Colonel Yazgar Shukr, a Kirkuk security official. A Kirkuk health official confirmed the death toll.

The death toll in Kirkuk was 16, the U.S. military said.

CURFEW

Mosques called for people to give blood. Reuters television footage showed Kirkuk's main hospital packed with wounded, some lying on a floor slick with blood because of a lack of beds.

Kurds in the ethnically mixed city say it should belong to the largely autonomous Kurdistan region, but Arabs and ethnic Turkmen want it to stay under central government authority.

A Turkmen member of the Kirkuk provincial council, Ali Mehdi, said armed demonstrators had attacked a Turkmen political office building.

Major-General Jamal Taher, Kirkuk's police chief, said demonstrators had sought refuge in the Turkmen office after the blast, but had been fired upon by the building's guards who thought they were coming under attack.

The situation had been brought under control, he added.

A curfew had been imposed on Kirkuk until Tuesday morning.

Last week, Iraqi President Jalal Talabani rejected the provincial election law as unconstitutional after Iraq's Kurdish lawmakers boycotted the parliament session that passed it. That has forced lawmakers to try to reach a compromise.

The law would have postponed voting in Kirkuk and it included an article carving out fixed seat allocations to each ethnic or sectarian group in the city.

Al Qaeda has exploited ethnic faultlines in Iraq's north, where it has sought