Abdulaziz Al-Muqrin and the others were reportedly killed as they tried to dispose of the body of U.S. hostage Paul Johnson.
State television said 12 others were arrested in the operation.
Hours earlier, Al-Muqrin's group said they had beheaded Johnson, and photographs of his severed head appeared on an Islamic website.
Correspondents say Al-Muqrin's killing -- although still denied by his group -- will be a coup for the Saudi government, which has been under intense pressure to stop a wave of attacks against Westerners in the kingdom.
Al-Muqrin was Saudi Arabia's most-wanted Al-Qaeda leader, and claimed responsibility for the shooting and hostage rampage last month in Khobar in which some 22 people were killed.
Reuters quoted an unnamed U.S. State Department official as praising the Saudi security forces' operation, saying it is a "telling demonstration" of the Saudis' commitment to defeating Al-Qaeda.
Johnson's killing and the swift retaliation came after the Saudi government refused to free Islamist prisoners by an 18 June deadline set by the U.S. engineer's captors.
The beheading brought condemnation from around the world. U.S. President George W. Bush said the United States will not be intimidated by what he called "these kinds of extremist thugs."
"There's no justification whatsoever for [Johnson's] murder. And yet they killed him in cold blood. And it should remind us that we must pursue these people and bring them to justice before they hurt other Americans," Bush said.
In Washington, Saudi foreign affairs adviser Adel al-Jubeir offered his condolences at a hastily called press conference.
"The people of Saudi Arabia are outraged by the cruel and cold-blooded murder of this innocent man. His murder has shaken us to the core. It is a terrible lie that the cowards who committed this inhumane act claim to be Muslim," al-Jubeir said. "There is no justification in our faith for harming the innocent."
And in Brussels, where EU leaders were wrapping up a summit, British Prime Minster Tony Blair said the killing shows that the United States and its allies must stand firm against terrorists.
"People who can do such a thing are not people we can negotiate with, they are people you simply have to defeat," Blair said. "And that's why we do make sure that we work with America in order to achieve this, and with our other allies as well."
The U.S. Embassy said more attacks are likely and the State Department warned U.S. citizens of a risk of violence across the Gulf region after urging many to leave Saudi Arabia this week.
But Secretary of State Colin Powell himself said yesterday he hopes foreigners will stay in Saudi Arabia, because their departure would be a victory for the militants.
State television said 12 others were arrested in the operation.
Hours earlier, Al-Muqrin's group said they had beheaded Johnson, and photographs of his severed head appeared on an Islamic website.
Correspondents say Al-Muqrin's killing -- although still denied by his group -- will be a coup for the Saudi government, which has been under intense pressure to stop a wave of attacks against Westerners in the kingdom.
Al-Muqrin was Saudi Arabia's most-wanted Al-Qaeda leader, and claimed responsibility for the shooting and hostage rampage last month in Khobar in which some 22 people were killed.
Reuters quoted an unnamed U.S. State Department official as praising the Saudi security forces' operation, saying it is a "telling demonstration" of the Saudis' commitment to defeating Al-Qaeda.
Johnson's killing and the swift retaliation came after the Saudi government refused to free Islamist prisoners by an 18 June deadline set by the U.S. engineer's captors.
The beheading brought condemnation from around the world. U.S. President George W. Bush said the United States will not be intimidated by what he called "these kinds of extremist thugs."
"There's no justification whatsoever for [Johnson's] murder. And yet they killed him in cold blood. And it should remind us that we must pursue these people and bring them to justice before they hurt other Americans," Bush said.
In Washington, Saudi foreign affairs adviser Adel al-Jubeir offered his condolences at a hastily called press conference.
"The people of Saudi Arabia are outraged by the cruel and cold-blooded murder of this innocent man. His murder has shaken us to the core. It is a terrible lie that the cowards who committed this inhumane act claim to be Muslim," al-Jubeir said. "There is no justification in our faith for harming the innocent."
And in Brussels, where EU leaders were wrapping up a summit, British Prime Minster Tony Blair said the killing shows that the United States and its allies must stand firm against terrorists.
"People who can do such a thing are not people we can negotiate with, they are people you simply have to defeat," Blair said. "And that's why we do make sure that we work with America in order to achieve this, and with our other allies as well."
The U.S. Embassy said more attacks are likely and the State Department warned U.S. citizens of a risk of violence across the Gulf region after urging many to leave Saudi Arabia this week.
But Secretary of State Colin Powell himself said yesterday he hopes foreigners will stay in Saudi Arabia, because their departure would be a victory for the militants.