Ten people were killed today when a Taleban timebomb ripped apart a minibus used to ferry Afghan workers to a military airport in Kandahar.

The blast during the morning rush hour killed seven people on the bus plus three bystanders and wounded 16 others.

It was the highest civilian death toll in months of attacks and came as 10,000 Afghan and coalition troops began a massive anti-Taleban operation across southern Afghanistan.

Elsewhere in the south, another three Afghans working for foreign organisations were killed in separate blasts as the Taleban turned its sights on softer targets.

A Taleban spokesman, Yusuf Ahmadi, said that the Kandahar blast had been caused by a timebomb.

"These people were working for the Americans, that is why we targeted them," he told the AFP news agency. "Anyone, anywhere in Afghanistan working for US forces will be targeted. They must quit working for Americans or their friends."

"The explosion was huge," said Tahir Shah, a witness who helped to carry three wounded people and five bodies from the minibus. Shops and vehicles nearby were damaged and blood and flesh were scattered at the site.

The blast coincided with the start of Operation Mountain Thrust, an anti-Taleban offensive in four southern provinces - Uruzgan, Helmand, Kandahar and Zabul. The operation will involve about 2,300 US forces, 3,300 British troops, 2,200 Canadians, about 3,500 Afghan soldiers and coalition air support.

The offensive is part of a major push to squeeze Taleban fighters responsible for a spate of ambushes and suicide attacks against coalition forces and Afghan authorities in recent months. It is also timed to coincide with the upcoming transfer this summer of command in the south from the US-led coalition to the Nato-led International Security Assistance Force.

"There is no scheduled end date to Mountain Thrust. The Coalition will continue operations well into the summer and until objectives are met," a US military statement said.

Jaap de Hoop Scheffer, the Nato Secretary-General, said yesterday that international forces could not be allowed to fail Afghanistan or it would again become a "training camp for terrorists".

Speaking to the Canadian television channel CBC, he said: "Suppose that Afghanistan would become the black hole again, the failed state it was or failing state under the Taleban. Where were the terrorists trained? In Afghanistan."

The offensive is focused on southern Uruzgan and northeastern Helmand, where the military says most of the militant forces have gathered. Operations were also to be conducted in the former Taleban strongholds of Kandahar and Zabul.

Troops yesterday built sand barriers and guard outposts around a small forward operating base in the Helmand district of Musa Qala, while others fired rounds from 119mm Howitzers deployed to the base’s perimeter into the vast desert expanse.

"We do it so they know it’s here and they know it could be pretty bad for them," said Lietuenant Colonel Chris Toner, commanding officer at the base 180 miles from Kandahar.

"This terrain up here favours the defender. I’m sure they know how many vehicles we have here, that we have artillery here, but that’s OK - I know what they know."

Limited operations began May 15 with attacks on Taleban command and control and support networks. According to US military and Afghan figures, about 550 people, mostly militants, have been killed since mid-May, along with at least nine coalition troops.

Yesterday, coalition and Afghan forces killed 26 suspected Taliban fighters in an attack on mountain positions in the eastern Paktika province.

Explore World News

• World Agenda

• Iraq News

• US & Americas News

• Europe News

• Middle East News

• Afghanistan News

• Asia News

• Africa News

• Ireland News

Times Recommends

• It’s only Brits who don’t appreciate me, says Blair
• Party’s over for Greek graspers
• White House tightens security for Xmas marathon