Violence across Iraq, including bombings against Shiites, killed 30 people on Wednesday as worshippers massed in a shrine city on the eve of major commemoration rituals often targeted by militants.

The bloodshed was the latest in a months-long surge in unrest that has forced Prime Minister Nuri al-Maliki to appeal for US help in combatting militancy, with Iraqi security forces having failed to stem the violence.

Bombings mostly struck north and west of Baghdad, targeting Shiite Muslims and members of the security forces.

On the outskirts of Baquba, north of the capital and one of Iraq's most violent areas, three coordinated bombs struck a gathering of Shiite pilgrims marking Ashura.

Eight people were killed and 28 others were wounded in the blasts, security and medical officials said.

Millions of Shiites from Iraq and around the world mark Ashura, which this year climaxes on Thursday, by setting up procession tents where food is distributed to passers-by and pilgrims can gather.

Some two million will make the pilgrimage, often on foot, to the Iraqi city of Karbala, which is home to a shrine to Imam Hussein.

Hussein, grandson of the Muslim Prophet Mohammed, was killed by the armies of the caliph Yazid in 680 AD and his death in Karbala has come to symbolise the split between Islam's Sunni and Shiite sects.

Tradition holds that the venerated imam was decapitated and his body mutilated. Throngs of modern-day Shiites beat their chests and self-flagellate during Ashura to express guilt for not coming to his aid.

Sunni militants linked to Al-Qaeda, who regard Shiites as apostates, often step up their targeting of Iraq's majority community during Ashura and the subsequent rituals of Arbaeen, including by attacking pilgrims.

Security measures have been stepped up, with more than 35,000 soldiers and policemen currently deployed to Karbala and surrounding areas, with concentric security perimeters barring vehicles from entering the city while helicopters hover overhead.

Two million pilgrims

Provincial authorities expect two million Iraqi and foreign pilgrims will have visited Karbala in the 10 days leading up to Ashura, with all of the city's hotels fully booked.

"I carry these iron weights every year, since I was 16 and until now," said Shawkat Hussein, a 60-year-old pilgrim visiting Karbala from Pakistan, referring to heavy iron chains hanging around his neck.

"What I am carrying does not compare to what Hussein did for his religion."

Shiites make up about 15 percent of Muslims worldwide. They are a majority in Iraq, Iran and Bahrain, and there are large Shiite communities in Afghanistan, Lebanon, Pakistan and Saudi Arabia.

Elsewhere in Iraq on Wednesday, attacks mostly targeting security forces killed 22 people, while police gunned down three militants in a raid.

East of the predominantly Sunni Arab city of Tikrit, a suicide bomber detonated a vehicle rigged with explosives at a police checkpoint, killing 11 people, including three policemen.

And near the former insurgent bastion of Fallujah, two bombs targeted the homes of policemen, followed by a third that went off as onlookers gathered at the scene, leaving four dead overall.

Violence around Baghdad and in northern Iraq killed seven others.

Wednesday's deaths were the latest in Iraq's worst violence since 2008, with more than 5,600 people killed this year, according to an AFP tally based on reports from security and medical officials.

Maliki has called for help from the United States in the form of intelligence-sharing and the delivery of new weapons systems in an effort to deal with the unrest.

Turkey's foreign minister also offered Ankara's assistance during a recent visit to Baghdad.

In addition to failing to curb the bloodshed, authorities have also struggled to provide adequate basic services such as electricity and clean water, and corruption is widespread.

Political squabbling has paralysed the government, while parliament has passed almost no major legislation in years.