(Reuters) -

A series of bombs killed at least ten people in mostly Shi'ite Muslim provinces of Iraq on Sunday ahead of the Muslim feast of Eid al-Adha, police and medical sources said.

Altogether 11 bombs were detonated by remote control. The deadliest attack took place in the city of Hilla, 100 km (60 miles) south of Baghdad, when two car bombs blew up in quick succession, killing at least five people, police said.

It was not immediately clear who was behind Sunday's attacks, which appeared to be coordinated, but Sunni Islamist and other insurgents, including al-Qaeda, have been regaining ground this year.

More than 6,000 people have been killed in acts of violence so far in 2013, reversing a decline in sectarian bloodshed that climaxed in 2006-07.

In Kut, four car bombs exploded separately, one of them near a primary school and another near a restaurant, killing at least two people and wounding 31, police said.

Leaflets signed by al-Qaeda's Iraqi affiliate have been distributed on the streets of the Baquba in recent days, telling residents not to send their children to school or they will be killed, residents and police said.

Last week, a suicide bomber drove a truck packed with explosives into the playground of a primary school in northern Iraq and blew himself up, killing 14 children along with their headmaster.

"The surge of violence in Iraq spares no one and no place," said a statement from the United Nations following that attack.

Two car bombs went off simultaneously near a vehicle repair workshop, killing two people in the city of Samawa, and a civilian was killed when a car bomb blew up in a commercial street on the southern outskirts of Baghdad, police said.

Forced underground in 2007, al-Qaeda's Iraqi wing has been re-invigorated by the civil war in neighboring Syria and growing resentment among the country's Sunni minority towards the Shi'ite-led government.

The affiliate, which merged with its Syrian counterpart this year to form the Islamic State of Iraq and the Levant, has claimed responsibility for attacks on both sides of the border.

(Reporting by Kareem Raheem in Baghdad, Aref Mohammed in Basra; Writing by Suadad al-Salhy; Editing by Sonya Hepinstall)