Islamic radicals in Saudi Arabia allied with al Qaeda said Saturday that they had kidnapped a U.S. military contractor in Riyadh, while in a separate incident, another American expatriate was gunned down at his house. The captive will be treated the way Iraqi prisoners were treated at the Abu Ghraib prison, the radicals said.

Calling itself al Qaeda in the Arabian Peninsula, the group said it was holding Paul M. Johnson Jr., 49, and posted a business card on the Internet that identified him as an employee of the Bethesda-based aerospace and defense giant Lockheed Martin Corp.

The group said in a statement that it was acting to "avenge U.S. mistreatment" of Muslim detainees. "We have our legal right to treat [American hostages] the same way they treat our people," the group said, mentioning the Iraqi prison where U.S. troops have mistreated detainees and the U.S. detention facility at Guantanamo Bay, Cuba, according to news service reports from Saudi Arabia.

The U.S. Embassy in Riyadh, the Saudi capital, said it was investigating the disappearance of an American in Riyadh but declined to disclose the person's name. In Washington, Lockheed Martin spokesman Dennis Boxx said the company had no immediate information about any employee being kidnapped and was checking the reports. Another Lockheed spokesman confirmed that a Paul M. Johnson works for the company in Saudi Arabia.

A man reached by telephone in Port St. John, Fla., said the description of the reported kidnap victim "sounds like" his father, who he said has been working in Saudi Arabia for about 10 years. "I'm trying to get a hold of the State Department," said the man, who is also named Paul Johnson. "Everybody's going nuts."

He said he last heard from his father about five days ago. "He's a good man," the son said.

Embassy officials earlier in the day confirmed the shooting death on Saturday of Kenneth Scroggs, 58, an employee of Advanced Electronics Corp., a Persian Gulf firm that does work for the Saudi military and other branches of the government. Saudi officials said Scroggs was fatally shot by unidentified gunmen at his home in Riyadh.

Witnesses told the Associated Press that three gunmen shot Scroggs in the back as he pulled his car into his garage, then shot him in the head from close range.

The violence was the latest in a series of attacks that military analysts say is designed to drive Westerners out of the desert kingdom and destabilize the Saudi government. The targeting of individual Americans and other Westerners in Saudi Arabia has intensified in recent days as the radicals have shifted their tactics from launching broad attacks on the country's oil industry.

On Tuesday, gunmen killed Robert C. Jacobs, 62, of Murphysboro, Ill., an employee of defense contractor Vinnell Corp., after following him to his home in Riyadh. On Saturday, an Islamic Web site posted video footage purporting to show that killing. The video shows a man who appears to be a Westerner fall to the ground in front of a garage as two men holding guns run toward him, the Reuters news agency said.

"The murder of the Jewish American Robert Jacob, who worked for the Vinnell espionage firm," a statement announcing the video on the Web site says.

The Saudi government has repeatedly promised to wipe out Islamic extremists who began a bombing and assassination campaign in the country 13 months ago. Security forces have arrested more than 300 people, but the number of attacks has increased in recent weeks.

On Saturday, Crown Prince Abdullah, Saudi Arabia's de facto ruler, again vowed to root out the radicals. "There is no doubt the devil is driving them and they are supported by those against Islam," he said in a statement.

More than 35,000 Americans work in Saudi Arabia, mostly in the oil industry and as military and technical advisers to the Saudi government. On April 15, the U.S. Embassy in Riyadh warned Americans to leave the country.

The al Qaeda statement, released late Saturday, said Johnson was targeted because he was one of four experts on the U.S. military's Apache helicopters known to be working in Saudi Arabia. "Everybody knows that these helicopters are used by the Americans, their Zionist allies and the apostates to kill Muslims, terrorizing them and displacing them in Palestine, Afghanistan, and Iraq," the statement said.

The Associated Press reported that a telephone number listed on Johnson's Lockheed Martin business card was the same as the number listed for Advanced Electronics Corp., Scroggs's employer.

The militants' statement said supporters had killed another American working as a defense contractor in his home in Riyadh, but it was unclear whether that reference was to Scroggs or Jacobs.

Staff Writer Martin Weil in Washington contributed to this report.