Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said the military is preparing to roll out evidence - such as date stamps on newly found weapons caches - that shows that recently made Iranian weapons are flowing into Iraq at a steadily increasing rate.
Mullen would not detail the evidence - which is expected to be unveiled by military leaders in Iraq as early as next week. But another senior military official said it will include mortars, rockets, small arms, roadside bombs and armor-piercing explosives - known as explosively formed penetrators or EFPs - that troops have discovered in caches in recent months.
The official, who spoke on condition of anonymity because the evidence has not yet been made public, said that dates on some of the weapons were well after Tehran signaled late last year that it was scaling back aid to insurgents.
In addition, the evidence will include information gleaned from detainees who were reportedly trained by members of Iran's elite Quds Force, as well as insurgents who received instruction on how to do the actual training.
Part of the firepower the military will unveil was used to support insurgents during the recent fighting in Basra in southern Iraq, officials said.
Mullen said he has seen evidence "that some of the weapons are recently not just found, but recently manufactured."
He also warned that the U.S. has the combat power to strike Tehran if needed.
Both Mullen and Defense Secretary Robert Gates have made clear that while all military options are on the table, they prefer at this point to use other pressures on Iran.
In laying out details of Iran's continued efforts to fuel terror in Iraq, U.S. military leaders are sending signals both to Tehran and Baghdad.
For Iran, the message is: the U.S. knows what Tehran is doing and will take action if necessary. For Baghdad, the hope is that Iraqi leaders will resist the negative influence from their Shiite brethren, and continue efforts to take control of their own country and crack down on Shiite extremists.
"The solution right now still lies in using other levers of national power, including diplomatic, financial and international pressure (against Iran)," Mullen said.
Still, while Mullen acknowledged that launching a third conflict in that region would be extremely stressful for U.S. forces, he said he has reserve capabilities in the Navy and the Air Force for any needed military action.
"It would be a mistake to think that we are out of combat capability," he said.
The latest findings, said Mullen, still do not prove that the highest leadership in the Iranian government has approved the stepped-up aid to insurgents who are killing U.S. and Iraqi forces.
But he said it appears that the leaders of the Quds Force are aware of the activity. And with their strong ties to Tehran's leaders, Mullen said, it's difficult to believe that "there isn't knowledge there as well."
Still, Mullen added: "I have no smoking gun that could prove the highest (Iranian) leadership is involved in this."
Mullen's comments came as military officials confirmed Friday that a ship under contract with the U.S. Navy fired flares and warning shots at small boats - believed to be Iranian - that approached a cargo ship in the Persian Gulf.
The Navy said that on Thursday two high-speed boats approached the ship, which is contracted by the U.S. to carry military cargo, but the boats turned away after the shots were fired. No injuries were reported.
U.S. military leaders have escalated their rhetoric against Iran of late, noting that suggestions last year that Tehran may have been backing off its support for militants have turned out not to be valid. Instead, Mullen said there also is recent evidence that Iran is continuing to train insurgents for the fight in Iraq.
"I just don't see any evidence of them backing off. And Basra highlighted a lot of that," Mullen said of Iran.
He would not detail any potential U.S. military options, and he played down any impending action.
"We have to continue to increase pressure, and I have no expectations that we're going to get into a conflict with Iran in the immediate future," said Mullen. "But I am concerned over time, just in these last couple years, that tensions continue to rise. Iran does not respond and, in fact they seem to be ratcheting it up in terms of their support for terrorism."
He said Iran has made it clear it wants to be a regional power, and he believes Tehran would prefer to see a weak Iraq, so it could significantly influence what happens there.
The Persian Gulf encounter involving the Navy is one of several similar episodes in recent months. Earlier this month, the USS Typhoon fired a flare at a small Iranian boat in the Gulf after it came within about 200 yards of the boat.
In January, several Iranian boats made what the Navy called provocative moves near a U.S. ship in the Strait of Hormuz. And in December the USS Whidbey Island fired warning shots at a small Iranian boat that officials said was rapidly approaching the ship.
Iranian officials have acknowledged several of the incidents, describing them as normal encounters and saying the boats did not threaten the U.S. vessels.