BAGHDAD (AP) - The U.S. military on Friday denied Iraqi government claims that the leader of al-Qaida in Iraq was captured and said a man with a similar name had been arrested in the northern city of Mosul.

Iraqi authorities had announced Thursday that police commandos captured Abu Ayyub al-Masri in a raid in the northern city of Mosul.

"Neither coalition forces nor Iraqi security forces detained or killed Abu Ayyub al-Masri. This guy had a similar name," said Maj. Peggy Kageleiry, a U.S. military spokeswoman in northern Iraq. She said no additional details were being immediately provided.

Iraqi Defense Ministry spokesman Mohammed al-Askari said the confusion arose because the commander of Iraqi forces in northern Ninevah province was convinced that he had arrested al-Masri - also known as Abu Hamza al-Muhajir.

"We called the commander of Ninevah operations 10 times and every time he insisted it was Abu Hamza al-Muhajir because when they caught him, they asked him whether his name was Abu Hamza al-Muhajir and he said yes," al-Askari told The Associated Press by phone.

He added that the commander repeatedly "insisted that it was him, how can we deny him then."

There had been false alarms in the past about al-Masri. At least twice - in 2006 and May 2007 - reports circulated that he was dead, but they were later proved wrong.

Al-Masri took over al-Qaida in Iraq after its leader, Abu Musab al-Zarqawi, was killed June 7, 2006 in a U.S. airstrike northeast of Baghdad.

U.S. officials said al-Masri - whose name means "The Egyptian" in Arabic - joined al-Qaida camps in Afghanistan in the late 1990s and trained as a car bombing expert before traveling to Iraq after the U.S.-led invasion in 2003. The U.S. military has $5 million bounty for al-Masri.

Meanwhile, the U.S. military on Friday said U.S. soldiers killed six Shiite extremists, who attacked U.S. forces with shoulder fired rockets and small arms, in several clashes in Baghdad's Shiite militia stronghold of Sadr City on Thursday.

Government envoys set strict demands for Shiite militias to end their battles against U.S.-led forces in Baghdad in meetings Thursday, but it was unlikely that militiamen would abide by the conditions.

Thousands of civilians already have fled Sadr City - home to nearly 40 percent of Baghdad's population - and aid groups say some areas are desperately short of food and medicine after seven weeks of street battles.

So far, the clashes are mostly confined to the southern part of the district where U.S. and Iraqi forces are building a barrier - reaching up to 12-feet high - to isolate it and disrupt supply and escape routes for militants.

"We really hope to block the north and the south," said Lt. Col. Tim Albers, an intelligence officer with the Multinational Force in Baghdad and the U.S. Army 4th Infantry Division, on Thursday.

The goal of the barrier is to put the "Green Zone," site of the Iraqi government and U.S. embassy, out of range for militia rockets and mortars.

"Within the next two weeks we should be done with the barrier part of the plan," Col. Allen Batschelet, the chief of staff for forces in Baghdad, said Thursday.

The military has said more than 700 rockets and mortars have been fired in recent weeks, but that number has since dropped to just a handful a day.

Except for Sadr City, the rest of Baghdad has been quiet. Since June 2007, there has been a 44 percent decrease in overall attacks by month in the rest of the capital and a 97 percent decrease in sectarian murders. The military did not supply exact numbers.

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Associated Press reporters Bushra Juhi and Qassim Abdul-Zahra contributed to this report from Baghdad.