British Army Major General J.B. Dutton, commander of the multinational division in southeastern Iraq, said smuggling of the deadlier weapons has been difficult to stop because of the long, open border between the two countries.
"I think we know from other reporting that the IED explosions, particularly the advanced technology ones, we believe the technology certainly is coming from across that border," Dutton told reporters at the Pentagon via a video link from Iraq.
Improvised Explosive Devices (IEDs) have become the top killer of coalition troops in Iraq, particularly in the Sunni dominated areas north and west of Baghdad.
A Pentagon task force with 1.5 billion dollars in funding has been trying to come up with solutions to the problem, but insurgents have managed to stay a step ahead by changing tactics and using weapons of increasing power and sophistication.
In relatively quiet Basra in southern Iraq, 18 people have been killed by the improvised bombs since August, said Dutton.
It was in that month that a weapons shipment seized near the Iranian border provided evidence that triggering devices and other materials used in the more advanced devices were coming into the country from Iran, according to US officials.
US intelligence concluded that the devices came from the Iranian Revolutionary Guard, US officials said at the time.
"I think we don’t know whether this is Iranian government policy or if this is splinter groups who are using Iran for their own purposes and not being controlled," Dutton said.
Among the deadliest of the new weapons are what Dutton called "explosively formed projectiles" which are shaped to blow a slug of hot copper through the armor on military vehicles.
He said coalition forces were trying to establish where the bombs are manufactured.
"We’re not completely certain where the manufacture takes place. We know where the technological know-how comes from, and we suspect where the parts come from," the British commander said.
The bombs are of varying grades of sophistication, with some requiring a simple workshop to build and others "a reasonably sophisticated factory," he said.
"Some are probably put together in country. Others may not be," he said.