BAGHDAD, Iraq - The U.S. military has detected a significant increase in the number of sophisticated roadside bombs in Iraq and believes that orders to send components for them came from the "highest levels" of the Iranian government, a senior intelligence officer said Sunday.

The officer, briefing reporters on condition he not be further identified, said that between June 2004 and last week, more than 170 Americans had been killed by the bombs, which the military calls "explosively formed projectiles." Those weapons are capable of destroying an Abrams tank.

The officer said American intelligence analysts believe the EFPs are manufactured in Iran and smuggled into Iraq on orders from the top of the Iranian government. He did not elaborate.

U.S. officials have alleged for years that weapons were entering the country from Iran but had stopped short of alleging involvement by top Iranian leaders.

The allegations were made in a briefing which had been set for last week. But U.S. defense officials said it was postponed so that the Pentagon could review the information.

That appeared aimed at avoiding the embarrassment suffered when evidence of Iraqi unconventional weapons presented by Secretary Colin Powell at the United Nations in 2003 proved to be wrong.

During the briefing, the officer said that one of six Iranians detained in January in a raid on an office in the northern city of Irbil was the operational commander of the Quds Brigade, a unit of the Iranian Revolutionary Guards that trains and equips Shiite militants abroad.

He was identified as Mohsin Chizari, who was apprehended after slipping back into Iraq after a 10-month absence, the officer said.

The Iranians were caught trying to flush documents down the toilet, he said. Bags of their hair were found during the raid, indicating they had tried to change their appearance, he added.