Judge Ahmed Faisal was headed home in his car in the city of Amara, the capital of Maysan province, when unknown assailants blocked his route and opened fire, a police officer told AFP on condition of anonymity.

A forensic source said the judge died of gunshot wounds to the head and chest.

Both sources said the victim had been shot 15 times with a Kalashnikov.

The killing was not immediately claimed.

In September, another anti-drug judge escaped an assassination attempt in the same province.

Security in the area has deteriorated, fuelled by tribal conflicts and a settling of political scores.

Parts of southern and central Iraq bordering Iran have become important drug trafficking routes in recent years.

Security forces have intensified efforts to crack down on the trade, often announcing drug seizures and the arrest of traffickers.

The interior ministry's anti-drug unit in December named Maysan and neighbouring Basra as the "leading southern provinces in terms of trafficking and consumption".

Drug consumption was rare in Iraq during the reign of dictator Saddam Hussein, with both users and dealers facing the death penalty if found guilty.

But after his 2003 ouster it boomed across Iraq, which had long been a transit route for drugs making their way into Europe from Afghanistan and Iran.