Two children, aged ten and 11, were wounded while planting a roadside bomb in a Shia village in Bahrain where a blast killed three policemen this week, police said this morning.

"A group of terrorists exploited these children by asking them to plant a home-made bomb" in Daih, state news agency BNA quoted a police official as saying.

He said one child was "seriously" wounded when the device exploded.

Police photos showed one child's fingers mangled by the blast and both boys' faces and bodies peppered with shrapnel.

Police said they have launched an investigation aimed at identifying those who incited the pair to plant the device.

Monday's explosion in Daih was the bloodiest attack on security forces since the Shia majority backed an uprising in February 2011 against the ruling Al-Khalifa family.

An officer from the United Arab Emirates was among the dead, making him the first officer from another Gulf state to be killed since forces from the region entered Bahrain in March 2011 to boost security personnel who later quelled the month-long uprising.

Public Security Chief Major General Tariq al-Hassan said in a statement that four more suspects in the "terrorist blast" have been detained, raising to 29 the number of arrests linked to the attack.

The kingdom remains deeply divided with persistent protests sparking clashes with police, scores of Shias jailed on "terror" charges and reconciliation talks deadlocked.

The International Federation for Human Rights says at least 89 people have been killed in Bahrain since February 2011.

Last year, the authorities increased the penalties for those convicted of violence, introducing the death penalty or life sentences for those convicted in cases that result in death or injury.