BAGHDAD — A fatal attack launched two days ago against the headquarters garrison of the American military in Iraq was carried out using a 240 mm rocket — a type of weapon provided to Shiite extremists by Iran, a U.S. general said Thursday.

One person was killed and 11 were wounded in the "indirect fire" attack Tuesday against Camp Victory, which includes the headquarters of Multinational Forces-Iraq.

The attack was overshadowed by congressional appearances by Gen. David Petraeus and Ambassador Ryan Crocker.

But such an attack with a sophisticated weapon against a nearly impregnable compound — far less vulnerable than the Green Zone in the heart of the capital — sends a strong message to the Americans that nowhere in Iraq are they safe — even in the nerve center of the U.S. mission.

It represents a major confrontation between the U.S. and armed Shiite groups the Americans insist are supported by Iran.

Maj. Gen. Kevin Bergner said the rocket was launched from a populated area in the Rasheed district of west Baghdad, which he said was infiltrated by breakaway factions of the Mahdi Army militia of anti-U.S. cleric Muqtada al-Sadr.

Bergner said the rocket was a type of weapon that Shiite groups "have received from Iranian sources in the past and used against coalition forces." A 240 mm rocket was fired against a U.S. base south of the capital in mid-August.

"The Iranian... rocket is the only 240-millimeter rocket found or fired in Iraq to date, and Jaish al-Mahdi is the only group known to fire that rocket," Bergner said, referring to the Mahdi Army by its Arabic name.

Displaying a twisted piece of shrapnel from the attack, he said military exerts had so far determined that its markings and manufacture were "consistent with" Iranian produced munitions.

Camp Victory, a huge area near Baghdad International Airport, has occasionally come under fire, but attacks with such a large number of casualties and with such sophisticated weapons are rare.

Bergner would not say where the rocket hit and would not speculate what part of the base the insurgents were targeting.

In Washington, Petraeus said the U.S. military had "very, very clear" evidence of Iranian involvement in such attacks.

"It certainly has contributed to a sophistication of attacks that would by no means be possible without Iranian support," Petraeus said at a news conference Wednesday. "Rockets — very particularly 240-millimeter ... there's no question where they have come from."

Iranian President Mahmoud Ahmadinejad rejected the congressional testimony by Petraeus and Crocker that accused Iran of interfering in its neighbor.

"Iran has no need to interfere in Iraq. The Iraqi government and nation are close friends of Iran," he said.