Foreign militants are thought to be behind a spate of deadly suicide bombings in Afghanistan, the country's defence minister has told the BBC.
Wardak fears more attacks may be being planned
Rahim Wardak said there was widespread assumption of collaboration between Afghan Taleban rebels and al-Qaeda, but no physical evidence of a link.
He admitted suicide bombs were a new phenomenon for Afghanistan and voiced fears that more attacks are planned.
The cities of Kabul and Kandahar have been hit by three bombings this week.
"We have to investigate further and see how the situation develops in the future, but we do have reports that there are more suicide bombers," Mr Wardak said.
Earlier, Mr Wardak told the Associated Press news agency that a number of Arabs and other foreigners had been known to have crossed into Afghanistan.
He cited similarities between the methods of attack commonly used in Iraq and those used recently in Afghanistan.
"Physically we do not have evidence to establish contact between al-Qaeda and the Taleban," Mr Wardak told the BBC.
"But people assume [a link] because of their previous relations, and because of tactics copied from Iraq and other places."
Afghanistan has been hit by nine suicide attacks in two months
He insisted that Afghans would not commit suicide because of traditional religious beliefs, and confirmed that some foreigners had been captured after involvement in other attacks.
On Wednesday a suicide bomber rammed a car into a convoy of US and Afghan troops, killing at least three civilians, officials have said.
That attack came after two blasts on Monday in the capital, Kabul, which killed nine people.
Five Afghan soldiers were also killed in a bomb blast in Pakhtia province on Wednesday.