June 20 (Reuters) - Al Qaeda militants are being targeted in a major U.S. offensive involving 10,000 troops around Baquba in Diyala province north of Baghdad. Al Qaeda in Iraq is one of a number of groups in Iraq linked to or led by al Qaeda. Here are five facts about the Sunni Islamist group, blamed for large-scale suicide bombings and mass kidnappings in Iraq: * U.S. President George W. Bush and General David Petraeus, commander of U.S. forces in Iraq, have called al Qaeda "public enemy number one" in Iraq. U.S. officials until recently had called Shi'ite militias the biggest threat to security. * Al Qaeda in Iraq was headed by Jordanian militant Abu Musab al Zarqawi until he was killed in a U.S. air strike in June 2006. He was replaced by close associate Abu Ayyab al-Masri. Iraq's Interior Ministry said in May that Masri, an Egyptian also known as Abu Hamza al-Muhajir, had been killed but soon after al Qaeda released an audio tape purportedly of its Iraq leader, who has a U.S. bounty of $5 million on his head. * Al Qaeda draws militants from across the Arab world. It makes up only a small proportion of the Sunni Arab insurgency in Iraq but its spectacular suicide bombings kill the most people. In the past year, Sunni politicians and U.S. officials have said it accounted for between 2 and 5 percent of total resistance. In October, the al Qaeda-led Mujahideen Shura Council said it had set up the Islamic State of Iraq, an umbrella group of Sunni militant affiliates and tribal leaders led by Abu Omar al-Baghdadi. In April it named a 10-man "cabinet", including Masri as its war minister. * A U.S. security crackdown in Baghdad, launched in February, forced many militants out of the capital into nearby Diyala and Salahaddin provinces. The U.S. military's Operation Arrowhead Ripper is targeting al Qaeda car bomb networks that cause carnage in Baghdad. * Al Qaeda has been involved in a power struggle with Sunni Arab tribes in western Anbar province after U.S. forces adopted a new strategy of arming and training local tribesmen as provincial police in the fight against al Qaeda. It has also fought pitched street battles with the Islamic Army in Iraq, a large group of mainly supporters of Saddam Hussein and ex-army officers, for control of the Baghdad suburb of Amiriya.
