U.S. forces in Iraq have captured a man officials describe as the "number 3" leader of Ansar al-Islam (search), an extremist group suspected of having ties to Usama bin Laden's Al Qaeda network, Fox News confirmed Tuesday.

Aso Hawleri was captured late last week in Mosul "without significant resistance," senior Defense officials told Fox News. The Associated Press, which first reported the capture, said Hawleri was taken into custody by soldiers of the 101st Airborne Division (search).

Most of Ansar al-Islam's leaders were believed to have fled their stronghold in northern Iraq before U.S. forces invaded in March. U.S. and Kurdish forces destroyed the group's main base in the early weeks of the war.

Ansar had taken control of a slice of the Kurdish-controlled area near the Iranian border, enforcing a version of Islam only slightly less stringent than the Taliban in Afghanistan. Their mountain strongholds were in an area not controlled by Iraqi government forces.

The Kurdish-Arab extremist group carried out suicide bombings, car bombs, assassinations and raids on militiamen and politicians of the secular Kurdish government, killing scores of people over the last two years.

U.S. officials say Ansar sent about a dozen people through Al Qaeda (search) camps in 1999 and 2000 and experimented with biotoxin ricin in 2002.

In late August, Gen. John Abizaid, commander of all forces in Iraq, told reporters that elements of Ansar al-Islam had migrated south into the Baghdad area, presenting an increased terrorist threat.

It remains unclear whether Ansar has played a role in any of the recent terror-style bombings in Iraq, including the Aug. 19 bombing of the U.N. headquarters in Baghdad that killed 22 people.

Ansar's top leader, Mullah Krekar (search), was taken into custody in the Netherlands in September 2002 and later deported to Norway. He was released from a Norwegian jail last April after a court found insufficient grounds to hold him on terrorism charges. Police dropped the charges in July, but are investigating him for allegedly financing terrorist activities.

The Associated Press contributed to this report.