Gunmen fired a rocket at a convoy carrying Britain's No. 2 diplomat in the capital of Yemen on Wednesday, damaging a car and wounding four people amid heightened fears about growing al-Qaeda influence in the impoverished Arab nation.

There was no immediate claim of responsibility for the attack, but Yemeni authorities recently boosted security around embassies in San'a after receiving information that the terror network was planning an attack.

The diplomatic car was on its way to the embassy with five staff members on board when it came under fire, Britain's Foreign Office said in a statement. One embassy official suffered minor injuries and was undergoing treatment, while the rest were unharmed, the statement said.

A Foreign Office official said the embassy's deputy chief of mission was in the car, but not injured. The official spoke on condition of anonymity in line with department policy.

Swift condemnation

The violence drew swift condemnation from British Foreign Secretary William Hague.

"This shameful attack on British diplomats will only redouble Britain's determination to work with the government of Yemen to help address the challenges that country faces," Hague said. He added that the violence also highlighted "the risks our diplomats face working for Britain's interests abroad."

The embassy's armoured car was struck by shrapnel and three bystanders also were wounded, a Yemeni security official said, speaking on condition of anonymity because he was not authorized to speak to the press.

A Yemeni who arrived at the scene after hearing the explosion said he saw two people fleeing after the blast.

"They were wearing a shirt and they did not have their face covered," Ali Mossad told Associated Press Television News. "Next to the site we found a bag with parts of the weapon launcher."

The attack came a day after a visit by third-ranking U.S. diplomat William Burns to discuss the security situation and less than six months after a suicide bomber attacked the British ambassador's car in San'a.

The violence has cast doubt on the effectiveness of the Yemeni government's U.S.-backed campaign against al-Qaeda militants, who have found a haven in parts of the rugged, mountainous nation where the central government's control is weak.

In April, the British ambassador was targeted by a suicide bomber who blew himself up near the diplomat's armoured car in a poor neighbourhood of the capital. The ambassador was unharmed. Wednesday's attack took place in the same neighbourhood of San'a, near the British Embassy.

French citizen shot

In separate violence Wednesday, a gunman shot and killed a French citizen employed by the French engineering company SPIE and working for the Austrian oil and gas company OMV outside the Yemeni capital, the French Foreign Ministry and Yemeni officials said.

A Yemeni security official said the attacker was believed to be a security guard at the company's compound outside San'a, but the motive was not immediately clear.

The Frenchman died shortly after being transferred to a hospital, the official said, speaking on condition of anonymity because he was not authorized to speak to the press.

Yemen says it is waging an aggressive campaign to uproot al-Qaeda, and Washington has earmarked some $152 million in military assistance to the government to help combat the threat with training, equipment and intelligence help.

Burns said Tuesday that the U.S. will continue to support its fight against terrorism.

Al-Qaeda in the Arabian Peninsula, an offshoot of Osama bin Laden's terror network, was formed more than a year ago when Yemen and Saudi militant groups merged. Al-Qaeda fighters are believed to have built up strongholds in remote parts of the country, allying with powerful tribes that resent the government of President Ali Abdullah Saleh.

The group's fighters attacked the U.S. Embassy in San'a twice in 2008, and earlier this year a number of Western embassies, including the U.S. and British, shut down for days in response to threats of attack.

The Nigerian suspect in the failed Christmas Day plot to bomb a Detroit-bound airliner has said he received training from al-Qaeda militants in Yemen, according to U.S. investigators. In February, the offshoot's military commander, Qassim al-Raimi, warned of further attacks against Americans.