The top U.S. military officer said Tuesday the discovery that roadside bombs in Iraq contained material made in Iran does not necessarily mean the Iranian government was involved in supplying insurgents.

The comments by Gen.Peter Pace, chairman of the Joint Chiefs of Staff, called into question assertions by three senior U.S. military officials in Baghdad on Sunday who said the highest levels of Iranian government were responsible for arming Shiite militants in Iraq with the bombs, blamed for the deaths of more than 170 troops in the U.S.-led coalition.

White House spokesman Tony Snow said Monday he was confident the weaponry was coming with the approval of the Iranian government.

Pace told reporters in the Indonesian capital, Jakarta, that U.S. forces hunting militant networks in Iraq that produced roadside bombs had arrested Iranians and 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," Pace said. "What it does say is that things made in Iran are being used in Iraq to kill coalition soldiers."

On Monday, 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," Pace told the Voice of America.

Iran denied it gave sophisticated weapons to militants to attack U.S. 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," Foreign Ministry spokesman Mohammad Ali Hosseini told reporters in Tehran.

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 that runs from the president to the secretary of defense to commanders in the field.