The US military says the highest-levels of Iran's government have ordered that insurgents in Iraq be supplied with sophisticated roadside bombs.
A senior US defense official in Baghdad says the Iranian-made bombs have killed at least 170 coalition troops in Iraq since 2004.
The official, who requested anonymity, blamed the al-Quds brigade of Iran's Revolutionary Guards for ordering that bombs be sent to Iraqi extremists.
Last week, US Defense Secretary Robert Gates said the Bush administration has evidence that Iran has provided weapons or technology to insurgents in Iraq.
US officials have called on Iran to "cease and desist" any meddling in Iraq. The Bush administration has warned that it will move against Iranians in Iraq who endanger U.S. and Iraqi troops.
In other news, Iraqi police say a suicide truck bomber killed at least 15 people and wounded more than 20 at a police station in northern Iraq.
Elsewhere, police say gunmen killed eight border guard recruits as they were riding a minibus in northwestern Iraq.
And witnesses north of Baghdad say a US Apache helicopter was shot down near an American air base (Taji). A US spokeswoman said the military is checking into the report.
Six US helicopters have gone down in Iraq in recent weeks. The US says four of them were shot down.