At least 50 people died in a spate of explosions across Iraq on Thursday, including 45 in twin suicide car bombs that rocked the holy city of Karbala, the third major attack in as many days.

The attacks mostly targeted pilgrims marking the Shia Muslim mourning day of Arbaeen, and were the latest in a series of bombings that have shattered a relative calm in Iraq following the formation of a new government last month.

In Karbala, home to the shrines of two revered Shia Muslim imams, two suicide bombers detonated vehicles packed with explosives 20 minutes apart, the head of Karbala provincial council Mohammed Hamid Al-Mussawi said.

The first attack struck at Karbala's northern outskirts at around 3:00pm, Mussawi said, with the second explosion occurring at around 3:20pm some 15 kilometres (nine miles) south of the city.

"At least 45 people, including women and children, have been killed and 150 have been wounded," he said.

Earlier on Thursday, a roadside bomb detonated among a crowd of Shia pilgrims at the Al-Rasheed vegetable market in southern Baghdad, killing one and wounding nine, while another such blast in a central Iraqi town killed one and injured three, an interior ministry official said.

The groups of pilgrims were walking to Karbala, 110 kilometres (70 miles) south of the capital, as part of ceremonies to commemorate Arbaeen, which marks 40 days since the anniversary of the death of the 7th century Imam Hussein, who is revered among Shia Muslims.

More than a million pilgrims are expected to visit Karbala in the coming days to commemorate Arbaeen, set to climax on Tuesday.

Also on Thursday, a suicide bomber blew up an explosives-filled car at a police headquarters in the central city of Baquba, killing two policemen and a female journalist in the third attack on Iraqi security forces in three days.

The suicide bomber detonated his payload at around 10:00am, just 200 metres (yards) from the site of a large suicide car bomb against another security agency Wednesday morning.

"I heard a massive blast and suddenly, there was a rain of shrapnel falling from the sky," said Murtada Aiseh, a 47-year-old local government employee who was in a nearby market with his wife and suffered head injuries.

"I woke up in the hospital and found my wife near my bed, she suffered injuries to her right hand."

The attack left three dead -- two guards for the headquarters and the journalist -- and 30 wounded, according to Ahmed Alwan, a doctor at Baquba hospital.

An interior ministry official, speaking on condition of anonymity, confirmed the toll.

The journalist, Wejdan Assad Al-Juburi, had been a reporter for the Iraq Al-Mustaqal (Independent Iraq) newspaper.

Alwan added that among the wounded were seven policemen, including a captain, two women and a young child.

Diyala was an Al-Qaeda stronghold as recently as 2008. While violence has dropped off dramatically both in Diyala and nationwide since then, the province remains one of Iraq's least secure.

Thursday's violence comes a day after attacks in Diyala killed 16 people, including 14 from a suicide attack at the offices of the agency responsible for securing government buildings.

That came a day after a suicide bomb at a police recruitment centre in the central city of Tikrit killed 50, the deadliest single attack to hit Iraq in more than two months.

The attacks come amid a spike in violence in Iraq, with at least 116 people killed and hundreds more killed in bombings in the past three days.

By contrast, 151 people were killed throughout December 2010, which marked the fifth consecutive month to see a decline in the number of people killed in violence.

The Tikrit blast was the first major strike since Prime Minister Nouri Al-Maliki named a new cabinet on 21 December, ending nine months of stalemate after 7 March parliamentary elections.

He has yet to name an interior, defence or national security minister, however, leaving him temporarily in charge of Iraq's entire security apparatus.