SANAA (Reuters) - Masked gunmen shot dead a Yemeni man who worked in the security office of the U.S. Embassy in Sanaa on Thursday, in an attack a Yemeni security source said appeared to be the work of al Qaeda.

The incident was the latest of a wave of attacks on officials in the impoverished Arab state, which is battling Islamist militants with Washington’s help.

The attackers, on a motorcycle, opened fire on Qassem Aqlan - who headed an embassy security investigation team - near his house in the center of Yemen’s capital, the source told Reuters.

“This operation has the fingerprints of al Qaeda which carried out similar operations before,” said the source, who asked not to be named.

Yemen-based Al Qaeda in the Arabian Peninsula (AQAP) and other militant groups strengthened their grip on parts of the country during an uprising that ousted veteran President Ali Abdullah Saleh in February.

Washington, wary of the growing power of al Qaeda, has stepped up drone strikes on suspected militants, with the backing of Saleh’s successor, President Abd-Rabbu Mansour Hadi.

A neighbor who identified himself only as Fahad said he had noticed strangers roaming the streets over the past three days, suggesting Aqlan was being watched before the attack.

“Once he (Aqlan) stepped out of his house the men shouted his name and when he replied, they shot him in the head and neck,” he said.

Aqlan, who was in his 50s and had worked at the embassy for more than a decade, was responsible for coordinating security information between the U.S. Embassy and the Yemeni authorities, the source added.

In Washington, U.S. State Department spokeswoman Victoria Nuland said that his main duties included conducting personnel checks as head of the “foreign service national investigative unit” and serving as a liaison with Yemeni security services.

He worked within the office of the embassy’s “regional security officer,” who is responsible protecting the embassy, its personnel and information.

She also said initial reports that he was involved in the investigation into the attack last month on the U.S. Embassy by protesters angry over an anti-Islam film made in the United States were incorrect.

“We condemn this vicious act in the strongest terms,” the spokeswoman said but declined to comment on who may have been behind the attack or why Aqlan may have been targeted, saying it may or may not have had anything to do with his work.

There have been a number of killings and assassination attempts on security officials and politicians since Yemen’s army drove Islamist fighters out of several southern towns earlier this year.

Last month Abdulilah Al-Ashwal, a senior intelligence official, was killed in a drive-by shooting in Sanaa.

Restoring stability in Yemen has become an international priority due to fears that al Qaeda could become further entrenched in a country which flanks oil producer Saudi Arabia and lies along major international shipping lanes.

AQAP, regarded as al Qaeda’s strongest regional wing, has mounted operations in Saudi Arabia and tried to launch attacks against the United States.