Four Nato soldiers have been killed and four injured in a suicide car bomb attack on their armoured convoy in southern Afghanistan today.

In a separate incident, a Canadian Nato soldier was shot and killed while on foot patrol near Kandahar.

In the first attack, members of the International Security Assistance Force (Isaf) were targeted by a suicide car bomber as they were travelling on the main road from Kandahar to Herat .

The armoured convoy was passing through the town of Girishk in Helmand province, a region which produces half the world's opium and where the Taleban are very active.

Local residents said that the explosion occurred during the morning rush hour near the town's main bazaar, among people travelling to work by motorbike and on foot.

Feda Mohammed Khan told the police that the road had been blocked off by police, but that he could see the scattered remains of the car used by the attacker. "I saw Afghan police carry three men wounded to their vehicles and take them to hospital," said Mr Khan.

Mohammad Hussain Andiwal, the Helmand police chief, said that three civilians were killed and seven wounded in the explosion. "It was a busy hour of the day when everyone was going to their work," he said.

Yousuf Ahmadi, a Taleban spokesman, said that the attack had been carried out by a Taleban recruit.

Officials at the Isaf office have confirmed the death toll but have not so far issued a statement or released the nationalities of the dead troops.

Most of the soldiers in Helmand are British, but a UK military spokesman said that he had not been informed that any of the victims was British. There are also Danish, Czech, Estonian and US soldiers serving in the province.

"As yet all I can say is that there were Isaf casualties," said Lieutenant-Colonel Simon Miller. "We are still waiting for confirmation of nationalities and types of casualties. I am not aware of four British soldiers being killed, that is wrong."

The fifth Nato casualty was a Canadian soldier on dismounted patrol in Panjwayi, about 20 miles (35km) west of Kandahar — an area that has seen intense clashes between security forces and the Taleban in the past but has been quiet recently.

The 2,500 Canadian troops and Afghan Army forces in the area have made a policy of carrying out foot patrols, to “show their presence, monitor the security situation and interact with the local population”, the Canadian military contingent said in a statement.

Opium and heroin grown in Helmand provide much of the funding for the Islamist extremist rebels who are trying to overthrow the Afghan Government and dislodge the Nato troops attempting to pacify the country.

Last year the Taleban staged more than 160 suicide attacks. More than 8,000 people were killed in 2007 as a result of the insurgency, including 1,500 civilians.

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