An intelligence analyst in the group said Iran was working through "multiple surrogates" - mainly in the Mahdi Army - to smuggle the EFPs into Iraq. He said most of the components are entering the country at crossing points near Amarah, the Iranian border city of Meran and the Basra area of southern Iraq.

The analyst said Iraq's Shiite-led government had been briefed on Iran's involvement and Iraqi officials had asked the Iranians to stop. Al-Maliki has said he told both the US and Iran that he does not want his country turned into a proxy battlefield.

"We know more than we can show," said one of the senior officials, when pressed for tangible evidence that the EFPs were made in Iran.

US officials have alleged for years that weapons were entering the country from Iran but had until Sunday stopped short of alleging involvement by top Iranian leaders.

During the briefing, a senior defense official said that one of the six Iranians detained in January in the northern city of Irbil was the operational commander of the Quds Force.

He was identified as Mohsin Chizari, who was apprehended after slipping back into Iraq after a 10-month absence, the officer said.

The Iranians were caught trying to flush documents down the toilet, he said. They had also tried to change their appearance by shaving their heads. Bags of their hair were found during the raid, he said.

The dates of manufacture on weapons found so far indicate they were made after fall of Saddam Hussein - mostly in 2006, the officials said.

In a separate briefing, Maj. Gen. Jim Simmons, deputy commander of Multinational Corps-Iraq, said that since December 2004, US helicopter pilots have been shot at on average about 100 times a month and been hit on an average of 17 times in the same period.

He disclosed a previously unknown shootdown, a Blackhawk helicopter hit by small arms fire near the western city of Hit. The craft crash-landed but there were no casualties. Simmons was on board.

The major general said Iraqi militants are known to have SA-7, SA-14 and SA-16 shoulder-fired anti-aircraft missiles but none of the most recent five military crashes were caused by those weapons. He said some previous crashes had been a result of such missiles but would not elaborate.

North of Baghdad, a suicide truck bomber crashed into a police station, killing at least 30 policemen. A total of 76 people were killed or found dead across Iraq. The US military said Sunday a soldier was shot and killed the day before in volatile Diyala province northeast of the capital. A second soldier was reported killed Sunday in western Baghdad.

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