The highest-ranking US military officer has questioned the assertion that the Iranian government is directly involved in supplying weaponry to insurgents in Iraq.
The comments by Gen Peter Pace, chairman of the Joint Chiefs of Staff, called into question claims by three senior US military officials in Baghdad on Sunday.
Those officials said the highest levels of Iranian government were responsible for arming Shia militants in Iraq with the bombs, blamed for the deaths of more than 170 troops in the US-led coalition.
White House spokesman Tony Snow said yesterday he was confident the weaponry was coming with the approval of the Iranian government.
Gen Pace told reporters in Indonesia that US forces hunting militant networks in Iraq that produced roadside bombs had arrested Iranians and that some of the materials used in the devices were made in Iran.
"That does not translate that the Iranian government per se, for sure, is directly involved in doing this," Gen Pace said. "What it does say is that things made in Iran are being used in Iraq to kill coalition soldiers."
On Monday, Gen Pace said he had no firm knowledge that the Iranian government had sanctioned the arming of the insurgents.
"It is clear that Iranians are involved, and it's clear that materials from Iran are involved, but I would not say by what I know that the Iranian government clearly knows or is complicit," Gen Pace said.
The Joint Chiefs chairman is the senior military adviser to the president, but he commands no troops and is not in the chain of command.
Iran has denied it gave sophisticated weapons to militants to attack US forces.
"Such accusations cannot be relied upon or be presented as evidence. The United States has a long history in fabricating evidence. Such charges are unacceptable," a Foreign Ministry spokesman said.