By Ben Farmer in Kabul
Heavy weapons are continuing to stream across the Afghan border from Iran despite Barack Obama's attempts to enlist Tehran's help in fighting the insurgency, officials have said.
Border police say they are regularly intercepting consignments of anti-tank mines and mortars bound for Afghan militants fighting Nato-led forces.
One shipment seized on May 23 along Afghanistan's 580-mile western border contained dozens of anti-tank mines.
"That's a regular occurrence," the official told the Daily Telegraph. "It tends to be heavier weapons like mines and mortars rather than Kalashnikovs".
Quantities regularly run into the hundreds and the weapons are usually brand new he added.
Mr Obama has been working hard to enlist Iranian support in tackling rampant arms and opium traffic across the border.
Sources said both sides were prepared for a "fresh look" at co-operation after years of hostility caused by Tehran's nuclear programme, American support for Israel, and Iranian suspicion of the US wars in Iraq and Afghanistan.
Italy has invited Iran to a special summit of G8 foreign ministers being held in Trieste later this month to discuss Afghanistan and Pakistan.
However sources said Tehran was still "hedging its bets", with elements within the country believed to be supporting Afghan insurgents.
The Shia-Muslim dominated country has no wish to see extremist Sunni groups like the Taliban and al-Qaeda in Afghanistan but it remains deeply suspicious of the US presence.
International forces believe elements within the Iranian regime are either behind the smuggling or at least doing little to stop it.
The disclosure that weapons are still freely flowing across the border follows Afghan army claims that Iranian weapons were recovered from a notorious Taliban and drug trafficker haven in Helmand province.
A four day sweep last month to clear the town of Marjeh found 44 bricks of Iranian-made explosives and dozens of Iranian-made mortars.
The Iranian embassy and US embassy in Kabul both refused to comment on the claims.
A spokesman for the British embassy said Iran could play a positive role in Afghanistan, but support for the Taliban was "completely unacceptable".
He said: "This approach undermines its own interests, contributing to instability on its border with Afghanistan, which in turn strengthens the narcotics trade.
"Iran should recognise that the goals of the Afghan Government and international community in Afghanistan are in Iran's own interests."