Lt. Gen. Ray Odierno told journalists increased Iranian backing for Iraqi militants apparently started in March, CNN reported.

"I think as we talked about surging forces ... I think maybe Iran decided to surge more money, conduct a bit more training and surge a few more weapons into Iraq at the same time," Odierno said.

Odierno said U.S. and Iraqi troops have been working on securing Diyala Province, which borders Iraq, and its capital, Baquba, to "cut those lines" from Iran.

The Iranian government has denied any efforts to supply forces in Iraq.