Iranian leader Ayatollah Khamenei says it's not insurgents blowing up U.S. and Iraqi forces in Iraq, it's American and Israeli intelligence that want the Iraqi government to fail and the occupation of Iraq to continue. Khamenei, in a speech translated by the Middle East Media Research Institute (search), says, "If ... [U.S. forces] wanted to resolve the lack of security in Iraq, they could ... [T]here are indications ... that these acts of terrorism are the handiwork of American and Zionist espionage services."
He says the U.S. "foolishly" and "falsely" accuses Iran and Syria of letting insurgents cross into Iraq, insisting, "[Americans] are to blame. ... This is not mere speculation. This is actual information." As for what that information is, Khamenei didn't say.
When these guys start making accusations like this it sounds like they are trying to cover their own tracks. The scary thing is, some people will believe it.