BAGHDAD, Iraq — Iraqi security forces detained an aide to the leader of Al Qaeda in Iraq in a raid early yesterday at a gas station south of Baghdad, state-run television and a security official said.

The official, speaking on condition of anonymity because he was not authorized to speak to the press, said the aide to Abu Hamza al-Muhajir, also known as Abu Ayyub al-Masri, was one of two men arrested in the dawn raid.

The two suspects ran a gas station in Mahmoudiya, about 20 miles south of Baghdad, the official said, adding the returns from selling gas and other oil products on the black market were being used to finance the operations of local Al Qaeda in Iraq cells.

The official, who was involved in the raid, did not identify the two men, but added that the Masri aide had confessed to meeting the terror network leader the previous day in the Mahmoudiya area but that he could not tell investigators of his whereabouts because he was constantly on the move.

Mahmoudiya is a stronghold of the Sunni-led insurgency. While the town is dominated by Shiites, the farmlands around it are thought to harbor cells of Al Qaeda in Iraq blamed for suicide bombings in the area and attacks against Iraqi and American security forces.

There have been frequent reports by the American military and Iraqi authorities on the arrest of aides of Mr. Masri since he took over the terror network following the June 7 killing of his predecessor, Abu Musab al-Zarqawi.

Meanwhile, four American Marines were killed in fighting in Anbar province, the military said yesterday. The Marines died Wednesday from wounds sustained due to enemy action in two separate incidents west of Baghdad, according to a statement. The deaths raised to at least 3,114 members of the American military who have died since the Iraq war started in March 2003, according to an Associated Press count.