"On Friday, the leader Abd al-Aziz al-Muqrin was martyred along with three others...in an ambush carried out by the soldiers of the despot (in Saudi Arabia). They opened fire on
them in a sudden way which led to their killing," said a statement attributed to al-Qaida in the Arabian peninsula posted on the al-Qalaa website on Saturday.
"The Mujahidin are continuing the jihad that they have pledged to God and the killing of their brothers will not weaken their resolve but only increase their determination and commitment," it added.
The group had initially denied reports that al-Muqrin, 31, had been killed.
Clashes broke out between
Saudi security and al-Qaida
Al-Muqrin was accused of masterminding the seizure and killing of US engineer Paul Marshall Johnson.
Saudi security officials said a witness noted the licence plate number of a car - from which Johnson's body was dumped just outside Riyadh on Friday - and notified police.
Police stopped the car at a petrol station in central Riyadh and a shootout ensued in which al-Muqrin, Rakan Muhsan Muhammad al-Saykhan - the second most-wanted Saudi fugitive - and two other fighters were killed, Saudi officials said.
His killing, however, will most likely be seen by Washington as a positive step from the Saudi government, which has been under intense pressure to halt a wave of attacks against Westerners in the kingdom.
"The killing of al-Muqrin would raise our morale after the gruesome murder of the US victim Johnson," Saudi journalist Khalid Salih al-Shashri told Aljazeera.
"Johnson's beheading has gripped the Saudi public in a sense of grief," he added.
Johnson's captors killed him late on Friday night after the Saudi government rejected a 72-hour ultimatum.
Demands from al-Qaida included the release of hundreds of suspected al-Qaida members from Saudi jails and for all Westerners to leave Saudi Arabia.