New intelligence indicates that Iran is supplying Iraqi insurgents with some of their deadliest weapons -- and in Baghdad today, U.S. military commanders are expected to give information about Iran's role in attacks on American forces.
In presenting evidence that Iran is providing support and weapons that are killing American soldiers, a senior military official is expected to make good on a promise made to the U.S. ambassador to Iraq made weeks ago.
Watch "Good Morning America" anchor Diane Sawyer this week reporting from Iran, where she will interview Iranian president Mahmoud Ahmadinejad.
U.S. officials have already disclosed some of the evidence -- shaped charges, or explosively formed projectiles. When they explode, a molten core of copper can pierce some of the heaviest armor, even an Abrams tank.
So far, the evidence has focused on markings and serial numbers recovered from bomb fragments -- markings that indicate the charges were made in Iran.
"Well, I think that Iran is very much involved in providing either the technology or the weapons themselves for these explosively formed projectiles," said Defense Secretary Robert Gates.
While they account for a small percentage of roadside bombs in Iraq, they are very lethal.
Gates has cited other evidence of Iranian involvement, including documents captured when U.S. forces conducted a raid last month in northern Iraq and arrested six Iranians. Iraq's foreign minister Hoshyar Zebari said his government has yet to see evidence from that raid that implicates Iran.
"We haven't seen … so far … any hard evidence," Zebari said.
Even Gates stopped short of directly linking the Iranian government to weapons found in Iraq. The weapons could be sold on the black market to militant groups in Iraq.
When asked about U.S. claims, Iran's ambassador to Iraq Hassan Kazami Qumi laughed and asked a question of his own.
"Did you see this equipment?" he asked.
One concern for intelligence analysts has been who the Iranians are supplying the weapons to.
Iran's natural allies in Iraq -- Shiite Muslims -- are largely pro-American.
Iraq's Sunni Muslims have led the deadly anti-American insurgency but Sunnis, in large part, distrust Iran even more than they distrust the United States.
Whatever information is divulged today, many Iraqis and Americans will want to take a very close look at the evidence after discredited intelligence reports moved the country to war with Iraq in 2003 and brought us to where we are.