In the Department of Defense News Briefing on October 8, Colonel Tobin Green, commander of 1st Brigade Combat Team, 1st Cavalry Division of the US forces in Iraq reiterated that terrorist meddling of the Iranian regime in Iraq continues.
Part of the briefing in this regard is as follows:

Q(CNN): You had made a brief reference about Iranian influence in your sector. How much are you seeing of fighters that may have gone into Iran, for training or — and then come back in and set up in your sector? And how serious is the Iranian influence in your sector, compared to other parts in Baghdad?

COL. GREEN: We do see Iranian influence. We also see some influence of foreign fighters or insurgents, who have moved back and forth from other countries. I mean, I’ve seen some that have migrated in from Syria for example.

Many of our most important targets are individuals who have had some migration or spent some time outside of the country with one of these external actors.

We actually had a detention yesterday that involved a high-value target that had spent some time in Iran, in the not-too-distant past. So that does occur. Remember that my area of operations includes places like Sadr City.

So I don’t think it’s uncommon that we would have, you know, external influence, the migration of some weapons or materials that have their origin from abroad. You know, we have seen that. But we track it pretty effectively and we track it in conjunction with Iraqi forces.