"Iran still smuggles equipment and aid to terrorists across the border," AFP quoted the US commander in Iraq. "I find Iranian influence in Iraq unhelpful accross all domains — political, military, economic," he added.
"The Iranians also continue to train special group leaders and provide them opportunities to come back to Iraq."
Jacoby said that the infiltration of men and materiel by Arab insurgents from Iraq's western neighbor Syria was down considerably on previous years but remained a risk, the report said.
"In the past, we had foreign fighters crossing the border through Syria. That has been greatly reduced from hundreds to just a handful," he said.
"It still happens, they're still dangerous and it's still important to improve Iraqi security along the border."
Special groups is the term US commanders use to refer to groups that have refused to join the political mainstream and which they hold responsible for many of the reprisal killings carried out during the sectarian bloodshed of 2006 and 2007.