Authorities in Baghdad say Iraqi security forces have captured the leader of an al-Qaida terrorist cell allegedly responsible for a series of beheadings.

The government identified the cell leader as Mohammed Najam Ibrahim, and said he worked closely with Iraq's most-wanted fugitive, Abu Musab al-Zarqawi. He was arrested in Baquba, 60 kilometers north of the Iraqi capital.

An official statement issued Thursday did not indicate when the arrest took place, but said interrogators are seeking information that might lead them to other members of the al-Zarqawi organization. Iraqi officials say Mohammed Najam Ibrahim and his brother have carried out a number of beheadings and also have launched attacks against Iraqi security forces.

In Iraq's western al-Anbar province, U.S. military officials say a weeklong offensive to hunt down insurgents is moving ahead. They also reported another casualty - a U.S. Marine who was killed Thursday.