Briton killed in suicide attack

• NEW: In a separate incident, insurgents attacked a nonprofit organization in Kabul


• Security firm G4S says Briton killed in the blast was one of its staff


• Another victim was an Afghan national working at the British Embassy, UK says


• The Taliban claim responsibility for the suicide attack

(CNN) -- A suicide attack in the Afghan capital, Kabul, on Thursday morning killed five people and wounded 33 others, including at least four children, said Hashmat Stanikzai, a police spokesman said.

An explosive-laden car was detonated as a foreign embassy convoy was passing in the 9th District police zone, said Interior Ministry spokesman Sediq Sediqi.

The UK Foreign Office said two of those killed worked for the British Embassy.

One of the dead was a British national, a civilian security team member, and the second was an Afghan national working for the embassy, Foreign Secretary Philip Hammond said in a statement.

A second British member of the security team was injured, he said.

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"I condemn this appalling attack on innocent civilians supporting our diplomatic activity," Hammond said.

"This outrage brings home to us once again the courage and perseverance of the people of Afghanistan and members of the international community who support them, who have lived together through decades of conflict."

British security firm G4S confirmed in a statement that the security workers caught up in the blast were its staff and offered its condolences to their families and friends.

"An investigation into the incident is under way and therefore we are unable to comment further at this time," it said. "Next of kin have been informed and we will continue to provide them with support."

Police in Kabul had earlier said that at least one British diplomat was killed after a large explosion damaged a convoy of foreign embassy cars in the capital.

The Taliban have claimed responsibility for the attack.

Pictures from Mustafa Deveci, a witness at the scene, showed at least five vehicles damaged at the site of the blast with their windows blown out.

In a separate incident, armed insurgents attacked the office of a nonprofit organization in Kabul late Thursday. Security forces killed two of the three attackers, Stanikzai said.

A Nepalese national was injured, the police spokesman said. The Taliban issued a statement claiming responsibility for that attack, too.

CNN's Laura Perez-Maestro in London; Yousuf Basil in Atlanta; and Ehsan Popalzai in Kabul contributed to this report.