BAGHDAD: An Al Qaida-linked militant group in Iraq pledged support to the organisation's second-in-command, Ayman al-Zawahri, and vowed more revenge attacks for the death of Osama bin Laden at the hands of US forces in Pakistan.

In a statement posted on an Islamist website forum on Monday, the caliph of the Islamic State of Iraq (ISC), Abu Baker al-Baghdadi al-Husseini al-Qurashi, mourned bin Laden's death.

“I tell our brothers in Al Qaida organisation and on the top of them Sheikh Mujahid Ayman al-Zawahri ... be merry, you have faithful men in the Islamic State of Iraq who are following the right path and will not quit or be forced out,” he said in the statement.

“I swear by God, blood for blood and destruction for destruction,” he said in a clear reference to revenge attacks for bin Laden's death.

Zawahri, an Egyptian-born doctor who met bin Laden in the mid-1980s when both were in Pakistan to support guerrillas fighting the Soviets in Afghanistan, has long been considered Al Qaida's deputy leader.

Islamic State of Iraq is believed by intelligence analysts to have been created by Al Qaida in Iraq as a local umbrella group for insurgent organisations. Iraq's army and police have been on high alert for revenge attacks since bin Laden's killing by US commandos in Pakistan.

Iraq became an important battlefield for Al Qaida after the US-led invasion that ousted Saddam Hussein.

Security officials have said bin Laden's death earlier this month may have little practical impact on Al Qaida in Iraq, a weakened but still deadly Islamist insurgency that could launch strikes for the next decade.

Al Qaida in Iraq may seek immediate revenge for the killing of the world's most wanted man but in the long run probably will be more a thorn in the Iraqi government's side than a destabilising force, security officials said.

On Thursday, a car bomber killed more than 20 people and wounded 80 at a police building in the mainly Shia city of Hilla.