Updated at 5:30 p.m. ET: A masked gunman assassinated a Yemeni security official who worked for the U.S. Embassy in a drive-by shooting near his home in the capital Sanaa on Thursday, officials told The Associated Press.
Yemeni officials told the AP the killing bore the hallmarks of an attack by the al-Qaida offshoot in Yemen, but it was too early to determine whether the group was behind it.
The slain official was identified as Qassem Aqlani, a man in his 50s.
He was walking near his home in western Sanaa, when a gunman on a motorcycle opened fire at him and fled the scene. The embassy is located in eastern Sanaa.
In a statement, U.S. State Department spokeswoman Victoria Nuland said officials were "deeply saddened" by the killing. "We condemn this vicious act in the strongest terms possible and extend our deepest condolences to his family and friends at this difficult time," Nuland said.
"We are coordinating closely with the Yemeni authorities to investigate this attack and to help bring those responsible to justice."
Aqlani had been working as a Foreign Service national investigator at the embassy for the last 11 years, the State Department said.
Most recently, he was in charge of investigating a Sept. 12 assault on the U.S. Embassy by angry Yemeni protesters over the anti-Islam film.
Protesters stormed the embassy and set fire to a U.S. flag before government forces dispersed them with tear gas. That attack came one day after the killings of the Americans in Benghazi.
The assassination resembles other attacks recently that have targeted Yemeni intelligence, military and security officials.
Those attacks are believed to be in retaliation for a military offensive by Yemen's U.S.-backed government against Yemen-based Al-Qaida in the Arabian Peninsula (AQAP), which Washington considers the most dangerous offshoot of the global terror network.
AQAP has called for attacks on U.S. embassies in a bid to exploit the anti-American sentiment that has swept the Middle East and other parts of the Muslim world in the past month over an anti-Islam film produced in the United States.
Initially, the film was linked to an attack on the U.S. Consulate in the Libyan city of Benghazi on Sept. 11 which left four Americans dead including U.S. Ambassador to Libya Chris Stevens. U.S. officials said later the attack was not linked to the video.
AQAP praised the killing of U.S. diplomats in Libya, describing it as "the best example" for those attacking embassies to follow.
AQAP had taken advantage of a security and political vacuum created by last year Arab Spring-inspired uprising and seized territories and cities in the south. The government-led offensive has pushed the militants out to mountainous areas from where they have been staging suicide attacks and assassinations inside cities.
Two weeks ago, a top intelligence official, Col. Abdullah al-Ashwal, was also killed in a drive-by shooting in Sanaa.
The Associated Press and Reuters contributed to this report.
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