Hamed Jumaa Farid al-Saeedi, known as Abu Humam or Abu Rana, was arrested a few days ago, Mouwaffak al-Rubaie said, adding that his arrest also led to the capture or death of 11 other top al-Qaeda in Iraq figures and nine lower-level members.

He was the second most important al-Qaeda in Iraq leader after Abu Ayyub al-Masri, al-Rubaie said. Al-Masri succeeded Abu Musab al-Zarqawi, who was killed in a US airstrike north of Baghdad on June 7.

"We believe that al-Qaeda in Iraq suffers from a serious leadership crisis. Our troops have dealt fatal and painful blows to this organisation," the security adviser said.

Al-Saeedi was "directly responsible" for the person who carried out the bombing of a Shia shrine in Samarra in February, al-Rubaie added. The bombing inflamed tensions between Shia and Sunni Muslims and triggered reprisal attacks that continue still.

"Al-Saeedi carried out al-Qaeda's policies in Iraq and the orders of the slain al-Zarqawi to incite sectarian violence in the country, through attempting to start a civil war between Shias and Sunnis but their wishes did not materialize," al-Rubaie added.

After his arrest, al-Saeedi gave up information that led to the arrest or death of 11 top al-Qaeda in Iraq figures and nine lower-level members, he added. He would not reveal the identities of the others, or where al-Saeedi was captured, for security reasons.

After al-Zarqawi was killed, authorities obtained information about al-Saeedi indicating he had been operating in Salahuddin province, al-Rubaie said. He later moved south to northern Baghdad and had been operating outside Baqouba, the same area where al-Zarqawi was killed.

Al-Saeedi had been hiding in a residential building, the security adviser said. "He wanted to use children and women as human shields during the arrest, which is why the operation was based on a very precise military plan to preserve the lives of women and children in the building," al-Rubaie said, adding that there were no casualties during the arrest.

"Hamed al-Saeedi supervised terrorist groups that kidnapped people for ransom, and killed policemen after they received their salaries in order to finance terrorist operations," the security adviser said. "He used to order terrorist operations using mortars and roadside bombs, which led to the killing of several troops and innocent civilians."

He said al-Saeedi also supervised the creation of death squads and ordered assassinations, bombings, kidnappings and attacks on Iraqi police and army checkpoints.

"The operations were brutal and merciless," he said.

Al-Saeedi's capture "will affect al-Qaeda in Iraq and its operations against our people, especially those aimed at inciting sectarian strife," al-Rubaie said.