BAGHDAD: Suicide bombers and gunmen Thursday attacked a bus transferring convicts from a prison north of Baghdad, sparking fierce clashes with security forces that left at least 60 dead, police said.

The dead include 51 prisoners and nine policemen, according to an official at the country's Ministry of Law. Rescue sources said many of the dead were burnt beyond recognition.

“At least 60 people, prisoners and policemen, were killed in a suicide attack followed by several IEDs (improvised explosive devices) and shooting, “an interior ministry official told AFP.

It was not immediately clear who launched the assault, which targeted a security convoy escorting a bus that was transferring around 60 prisoners, many of them held on terrorism charges, from the main prison in Taji, some 25 kilometres (15 miles) north of Baghdad.

The attack took place at about 4:00 am, hours before UN Secretary General Ban Ki-moon was to hold talks with Prime Minister Nuri al-Maliki in an effort to spur international mobilisation against a jihadist insurgency.

It came a year almost to the day after militants attacked the same prison in Taji and another facility in Abu Ghraib, west of the capital, killing at least 20 members of the security forces.

Officials said at the time that no inmates had escaped from Taji prison.