Iran has been at war with the US since 1979. Her proxies have caused the death of more Americans than anyone besides al Qaeda, since that time. It is something the regimes admits in private and occasionally in public. While it has been clandestine, Iran's pursuit of nuclear weapons could make that war even more deadly.

Iran's current activity appears to be that of helping our enemies with logistical support. Attacking that logistical support has resulted in the capture of some Iranians in Iraq and may do so in Afghanistan. Iran has responded to that capture with a bogus hostage try against the Brits and the current arrest of Americans visiting Iran.

The only reason Iran has not used more effective means in its war with the US is it fears a US response. I'm not sure why they fear such a response since we seem to be going out of our way to even acknowledge Iranian responsibility for the logistical assistance to our enemies. I guess both sides fear the consequences that might flow from that acknowledgment. We have come along way from the original announcement of the Bush doctrine on states that support terrorism.