The US is offering a reward of up to $5 million to anyone providing information leading to Abu Ayyub al-Masri, the alleged senior al-Qaeda leader in Iraq.
Condoleezza Rice, the US secretary of state, on Friday authorised the reward under the Reward for Justice programme, which has paid more than $62 million to more than 40 people who have provided information to the US.
Al-Masri, also known as Abu Hamza al-Muhajir and born in Egypt, is believed to be the successor to Abu Musab al-Zarqawi, the leader who was killed in a US bombing raid near Baquba earlier in June. The US bounty for al-Zarqawi was $25 million.
Al-Masri is said to have trained in Afghanistan and formed al-Qaeda's first cell in Baghdad, according to the US military.
US officials claim he is an explosives expert trained in the construction of improvised bombs.
Adam Ereli, a spokesman for the state department, said: "We encourage anyone with information on al-Masri's location to contact the US embassy in Baghdad, any US military commander in Iraq, any US embassy or consulate, or the rewards for justice staff."
Earlier payments have included $30 million to people who gave tips that led to the 2003 killing of Uday and Qusay, the sons of Saddam Hussein, the former Iraqi president.