Group says it kidnapped American in Saudi capital
It also claims responsibility for killing another U.S. citizen
RIYADH, Saudi Arabia (CNN) -- A group linked to al Qaeda claimed Saturday to have kidnapped an American engineer in the Saudi capital.
Meanwhile, a Web site used by Islamic militants posted a video that purported to show the killing of an American worker in Riyadh on Tuesday. CNN has not confirmed the authenticity of the video.
And earlier Saturday, Kenneth Scroggs, an American engineer, was shot to death in the same city.
The group calling itself the Falluja Squadron posted a statement signed by the al Qaeda group of the Arab Peninsula on the Web site Voice of Jihad. The statement claimed to have taken an American hostage.
The U.S. Embassy in Riyadh confirmed only that the man is missing.
The statement identified the missing American by name and described him as a "specialist" and an engineer who works as a systems developer for the AH-64 Apache attack helicopter.
The group posted the man's driver's license, Saudi and American identification papers, and other documents on the site to prove he was taken hostage.
The statement said the United States and its allies have used the Apache helicopter in Afghanistan, Iraq and the Palestinian territories.
"We have our legal right to treat [hostages] the same way they treat our people," it adds. "We will publish more details about the man kidnapped and explain the mujahedeen's demands."
In a statement, deputy State Department spokesman Adam Ereli said "The American citizen has been reported missing. We are in contact with the family and working with Saudi authorities to locate the missing person."
Ereli said he had no details but that the State Department learned of the missing man about 1 p.m. ET when the family contacted the U.S. Embassy to report him missing.
Video of killing published online
The video published on the Islamist Web site is said to show the death of Robert Jacobs, a 63-year-old employee of Vinnell Arabia Corp.
Jacobs was gunned down at his home in the eastern Riyadh neighborhood of al-Khaleej, which contains several residential compounds for Westerners, according to Saudi police and Jacobs' company.
The man's face is never seen in the video, and there is no way to immediately confirm it is Jacobs, a native of Murphysboro, Illinois.
The video starts with Arabic text that reads, "The murder of the Jewish American Robert Jacob, who worked for the Vinnell espionage firm."
Pictures of wounded Arab children follow, then an 18-second clip that purports to show Jacobs' death.
The attack begins with men yelling, and then a series of 10 gunshots is heard. One attacker is seen holding a pistol and firing it at a man who falls to the ground after the first shot. The gunman then stands above the fallen man and continues to shoot.
There is an edit in the video after the shooting stops. Two men are seen bending over their victim, one of them making a sawing motion at the man's neck.
There has been no public indication from investigators that Jacobs was decapitated.
The video shows three attackers. Each is dressed casually, with the gunman wearing western-style sports shoes.
Saudi police said Jacobs was found dead in his home in the eastern Riyadh neighborhood of al-Khaleej, which contains several residential compounds for Westerners.
American shot to death
The Falluja statement also claimed that militants "managed to kill another American who is a manager in the same field" as the missing American. The victim worked for a British-Saudi company, the statement said.
On Saturday, the U.S. Embassy confirmed that a man shot dead in a drive-by shooting in the capital was an American. The embassy identified the shooting victim as Scroggs, but provided no other information.
Scroggs' killing is the third confirmed shooting death of a Westerner in Riyadh in a week. Jacobs was killed Tuesday, and a cameraman for the British Broadcasting Corp. was killed Sunday.
Saudi security sources said Scroggs was killed in the Malaz neighborhood in the central part of Saudi Arabia's capital.
He was parking his car at his home when he was shot in the back, police said. Three militants were believed to have been involved.
U.S. Ambassador to Saudi Arabia James C. Oberwetter offered condolences to the families of all the victims.
Residential security tightened
In light of the shootings, security has been tightened in residential compounds where many foreign workers live.
Earlier attacks -- including a hostage standoff in late May that ended with 22 captives killed -- have been blamed on Islamic militants battling the Saudi government.
On Monday, a statement by an al Qaeda affiliate in the region warning of more attacks was posted on two Islamist Web sites.
The message warns Muslims not to spend time with Westerners, to avoid being caught up in any attack, "as well as avoiding using all shapes and forms of transportation by them."
"All compounds, bases and means of transport, especially Western and American airlines, will be the direct target for our coming operations in the near future," the statement said.
The U.S. State Department has urged Americans to leave Saudi Arabia.
CNN's Caroline Faraj in Dubai contributed to this report.