A car bomb targeting Shiite Muslims in Iraq and the shooting of a lawyer and his family left 21 people dead on Wednesday, after Al-Qaeda warned it would target lawyers and retake territory in a new campaign.

The attacks were the latest in an apparent spike in unrest since the beginning of the Muslim fasting month of Ramadan, bringing to 90 the number of people killed so far this month.

In the deadliest incident on Wednesday, a vehicle packed with explosives ripped through a group of Shiite worshippers during a commemoration ceremony in Al-Tanmiyah village, around 50 kilometres (30 miles) southeast of Baghdad.

The 6:45 pm (1545 GMT) attack killed 13 people and wounded 30 others, according to a police lieutenant colonel and a medic, both of who declined to be identified. Most of the victims were men, the officials said.

It also sparked a large fire in a nearby market and damaged adjacent houses.

The gathering had been to mark the day that Imam Ali, a central figure in Shiite Islam and the cousin and son-in-law of the Prophet Mohammed, was wounded, days before his eventual death in 661 AD.

The blast struck just before the iftar meal that breaks the daily fast Muslims engage in during Ramadan.

Earlier on Wednesday, gunmen shot dead a lawyer, his judicial investigator son and six of their family members in a town north of Baghdad.

The shooting took place at the home of Khayrallah Shati, a lawyer in the town of Baiji, 200 kilometres (120 miles) north of the capital, killing him, his wife, five sons and another relative who was staying with them.

"Khayrallah Shati, his wife and five sons, and a family guest staying with them were killed early this morning in Baiji," a police officer said on condition of anonymity.

"Gunmen raided his house and opened fire on the family.... Initial reports are that this is a terrorist attack, but the investigation is still ongoing."

The officer said one of Shati's sons was a judicial investigator.

An official in the main hospital in Salaheddin provincial capital Tikrit said the facility received eight bodies -- seven men and a woman -- all with multiple gunshot wounds.

Al-Qaeda's front group, the Islamic State of Iraq, said in July that it was launching a "new military campaign aimed at recovering territory."

An earlier message posted on various jihadist forums said the ISI would begin targeting judges and prosecutors, and try to help its prisoners break out of jails.

The latest violence brings the number of people killed in attacks in Iraq this month to at least 90, including 47 security forces members, according to an AFP tally based on security and medical sources.

While violence has decreased from its peak in 2006 and 2007, attacks remain common across Iraq. There were attacks on 27 of the 31 days in July.

Official figures put the number of people killed in attacks in July at 325, the highest monthly death toll since August 2010.