By Alastair Leithead
BBC News, Helmand
A hi-tech bomb, similar to the ones used by militants in Iraq, has been found in the Afghan capital, Kabul.
The new type of bomb is an extra worry for Kabul security
Afghan intelligence sources say the bomb can penetrate heavily armoured vehicles and was set up by a road to target a high-level government convoy.
There is increasing evidence that sophisticated explosives technology is crossing into Afghanistan from Iraq.
Police and government officials say they believe Iran is the source of these so-called "shaped charges".
They have been used widely in Iraq and now it seems they are on the streets of Afghanistan.
These "shaped charges" are designed to explode in a specific direction, to concentrate the force into one point, and their discovery in Kabul is a worrying development for security forces.
A source from the Afghan intelligence agency said the bomb had been planted by a busy roadside in the centre of the capital but had been discovered before it was detonated.
He said the intended target was mostly likely a high-level government convoy.
Hi-tech charges have been found in Afghanistan close to the Iranian border before and senior police and government officials have told the BBC that Iran's security agencies are involved with supplying the Taleban insurgency with money, weapons and explosives.
In April, in the southern Helmand province, weapons of Iranian origin were found but there was no direct link to the government.
The Iranian ambassador to Kabul strongly denies any involvement.