By Charles Haviland
BBC News, Kabul
The Nato-led force in Afghanistan, Isaf, has confirmed reports that its soldiers shot two Afghan men on Sunday morning, killing one of them.
Mr Karzai says "extreme use" of force must stop
It said the men ignored warnings to stop at a barrier in the southern province of Helmand set up after the death of a British soldier.
The provincial police chief has said that the two men were civilians.
Isaf said the shooting was being investigated. It did not confirm or deny if the men were civilians.
According to Isaf, the two Afghan men drove their motorcycles towards the cordon, ignoring Isaf soldiers' warnings to stop.
It said its forces opened fire only after exhausting all reasonable measures.
One of the two men was killed and the other wounded in the incident near the Helmand capital, Lashkar Gah.
On the issue of whether the men were civilians, Isaf spokesman Lieut Col Charlie Mayo of the British army said: "This was a rural area with very few civilians around and we were supported by the Afghan National Police."
It has been confirmed that the soldier who had died in a blast at the site shortly the shooting incident was British. Four of his colleagues were injured.
Their armoured Land Rover had been escorting a military team surveying the site for a new road project.
Two Estonian Isaf soldiers died on Saturday in a missile attack in the same province.
After the death of an estimated 25 civilians in an air strike called by British forces on Thursday, President Hamid Karzai accused Isaf and the US-led coalition here of "extreme" and "disproportionate" use of force.
There are now several incidents each week of foreign forces killing civilians in Afghanistan.
He said the foreign forces had to start working in accordance with his government's wishes.
Nato said he had a right to be angry but added that no Isaf soldier intended to kill civilians.