Sixteen Al-Qaeda members, including five who have been sentenced to death, escaped during the night from a prison in the heart of Tikrit in central Iraq, a security official said on Thursday.
The group managed to remove the windows from a prison bathroom, crawled through the opening and scaled a ladder to climb over the prison wall, the official said.
"Sixteen prisoners from Al-Qaeda managed to escape from one of the prisons in the centre of Tikrit," said the official, who declined to be identified as he is not permitted to speak to the media.
One of the group was re-arrested Thursday morning but the remainder are still at large, he added.
Iraqi security forces, he said, have tightened security in Tikrit, a predominantly Sunni town 180 kilometres (110 miles) north of Baghdad in Salaheddin province that was once the stronghold of executed dictator Saddam Hussein.
US military commanders say that Al-Qaeda remains a dangerous threat in Iraq but insist that its attempts to establish an Islamic caliphate in the war-torn country have failed.