WASHINGTON (CNN) -- An increasing number of attacks using an Iranian-based explosive is undermining security in Iraq, a senior U.S. military commander said Wednesday.
U.S. officials say allegedly Iranian-made explosives are used by Iraqi militants.
The attacks come amid a diplomatic push by the United States to encourage Iranians to help improve the security situation in Iraq.
Lt. Gen. Raymond T. Odierno told CNN that weapons of Iranian origin, such as bombs called explosively formed projectiles, are making their way into Iraq.
There were 99 EFP attacks in Iraq in July -- the most since counting began in December, Odierno said. That type of explosive accounted for one-third of the 79 U.S. troop deaths last month, he said. The military says both parts for the weapons and the weapons themselves are being brought across the border.
The United States can't prove that Iran's central government is responsible for providing the weaponry, but officials have been saying for months that such activity is being conducted by Iran's Revolutionary Guards-Quds Force.
Iran officially has denied being involved in promoting insurgent activity, but some U.S. officials think the country's senior leaders must be aware of the activity if the Quds Force is involved. Watch how the U.S. is responding to evidence of Iranian weapons »
Asked about the EFP numbers, State Department spokesman Sean McCormack told reporters Wednesday that "we have not yet seen any positive results from the Iranians" and that at future meetings, "we will convey that we have not seen any positive developments."
Odierno said the United States is taking defensive action against the attacks, specifically by targeting Shiite extremist cells in Baghdad.
"We continue to go after these EFP networks in Baghdad and all over the country," he said.
Additionally, new armored vehicles are being shipped to Iraq. More than 17,000 are needed in Iraq, but right now there are only about 200, the Pentagon says.
Iran -- which says the huge border with Iraq is porous and has acknowledged that smugglers and black marketers do traverse it -- frequently likens the dilemma with problems the United States faces along its vast border with Mexico.
Military officials have said for weeks that they expect as many weapons as possible to be shipped from Iran to Iraq before September, when Gen. David Petraeus, the top U.S. commander in Iraq, and U.S. Ambassador to Iraq Ryan Crocker issue a report about progress there. The thinking is that Iran intends to make it look like the United States is not making any progress.
In addition to the Iranian-based explosives, military elements in Iran are also hurting Iraq's security, Odierno said.
Insurgents trained in Iran have been firing rockets and mortars at Baghdad's Green Zone with greater precision, and money from Iran is ending up in the hands of Iraqi insurgents, he said.
All of this comes as a thaw has unfolded between the United States and Iran, which have been meeting in Iraq to discuss security. The ambassadors have met and a subcommittee has been formed to deal with security matters that have popped up. Iraq has spearheaded the effort.
Officials have said the United States has made its position about Iranian involvement clear in the meetings, the last of which was Monday.
CNN's Barbara Starr, Charley Keyes and Aneesh Raman contributed to this report