The Times
Jerome Starkey in Kabul

Two British electricians were among 17 people killed when a car carrying a bomb rammed an armoured bus in Kabul, in one of the deadliest insurgent attacks of the ten-year war.

Witnesses said that the heavily armoured Rhino bus was thrown sideways by the force of the explosion and was engulfed in flames. At least 13 people on board the bus, including five soldiers and eight civilian contractors, were killed, Nato officials said. Two Afghan policemen and two civilian bystanders were also killed by the blast on Saturday.

The two British contractors were electricians employed by the Texas-based engineering company Fluor, it was confirmed yesterday. Their bodies were due to be repatriated last night.

Keith Stephens, a spokesman for Fluor, said: “The company has notified the families involved. Our thoughts and prayers are with the family, friends and loved ones of our co-workers. Right now our focus is helping them.” The attack, which came just 24 hours after a Pentagon report claimed that violence was down across Afghanistan, was one the deadliest single incidents for Nato’s International Security Assistance Force (Isaf), excluding air crashes.

The bus was part of a Nato convoy that had just left a training base on the southwestern edge of the capital, close to the ruined Darul Aman Palace, when a car packed with explosives swerved into its path.

One bystander said the truck was thrown 10 metres through the air, landing on its side. A second witness said he saw a passenger trapped inside the wreckage, while rescuers battled to quell the flames. US troops were later seen collecting debris from the blast, while smoke still smouldered from the remains of the bus. Around 165 civilian contractors are thought to have died in Afghanistan since 2001. Six of them were British, five of whom worked as security guards.

The Taleban claimed responsibility for the blast, which came on the same day that a renegade Afghan soldier attacked his Australian military mentors in the south of the country, killing three and wounding several. In a third incident, in the east of the country, a teenage girl detonated a suicide vest at the gates of the local intelligence agency, killing two guards.

US and Nato officials were discussing plans to hand more of the country over to Afghan security forces at the time of the attacks, as part of their plan to cease combat operations by 2014.

A spokesman for the insurgents said they used 700 kgs (1,540lb) of explosives in the Kabul bomb, to target soldiers training Afghan police.

A Canadian soldier, Master Corporal Byron Greff and a Kosovan contractor were among those killed on the bus, a Nato official said. He said four US soldiers and four US civilians were killed.

A spokesman for the British Embassy in Kabul said he could “confirm that two British nationals were among those killed in the attack in Kabul on Saturday.” He added that their next of kin had been informed. Underscoring the scale of the attack, President Karzai took the unusual step of offering his “heartfelt condolences” to the families of those killed.

“Afghan people are grieved by the Nato loss of lives and share the pain and sorrow with the families and friends of the troops killed,” he said in a statement, after meeting the US ambassador Ryan Crocker and the commander of US and Nato forces in Afghanistan, General John Allen.

General Allen had earlier said he was “outraged” by the bombings. “The enemies of peace are not martyrs, but murderers,” he said.

David Cameron, who was in Australia when he learned of the deaths, offered his condolences to the families of those killed. A similar attack on the same stretch of road killed 18 people — including five soldiers and an American colonel — in May 2010.