The US military has detected a significant increase in the number of sophisticated roadside bombs appearing in Iraq and believes that orders to send components for them came from the "highest levels" of the Iranian goverment, a senior intelligence officer said Sunday. The officer, briefing reporters on condition he not be further identified, that that between June 2004 and last week, more than 170 Americans had been killed by the sophisticated bombs, referred to by the military as "explosively formed projectiles." Those weapons are capable of destroying an Abrams tank. The officer said American intelligence analysts believe the EFPs are manufactured in Iran and smuggled into Iraq on orders from the top of the Iranian government. He did not elaborate. US officials have alleged for years that weapons were entering the country from Iran but had stopped short of alleging involvement by top Iranian leaders. The US officer said Iran was working through "multiple surrogates" - mainly "rogue elements" of the Shi'ite 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 US officer said American authorities had briefed Iraq's Shi'ite-led government on Iran's involvement and Iraqi officials had asked the Iranians to stop. Prime Minister Nouri al-Maliki, a Shi'ite, has said he told both the US and Iran that he does not want his country turned into a proxy battlefield. Last week, US officials said they were investigating allegations that Shi'ite lawmaker Jamal Jaafar Mohammed was a main conduit for Iranian weapons entering the country. Mohammed has believed to have fled to Iran. The allegations were made in a briefing which had been set for last week. But US Defense officials said it was postponed so that the Pentagon could review the information to make sure it was accurate. That appeared aimed at avoiding the embarrassment suffered when evidence of Iraqi weapons of mass destruction presented by Secretary Colin Powell at the United Nations in 2003 proved to be wrong. During the briefing, the officer said that one of the six Iranians detained in January in the northern city of Irbil was the operational commander of the Quds Brigade, a unit of the Iranian Revolutionary Guards that trains and equips Shi'ite militants abroad. 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 because bags of their hair were found during the raid, he added. He said the dates of manufacture on weapons found so far indicate they were made after fall of Saddam Hussein - mostly in 2006. He said the "machining" on the components was traceable to Iran but did not elaborate. However, US officials told reporters there was no indication Iranian weapons were behind the latest spate of helicopter crashes. Maj. Gen. Jim Simmons, deputy commander of Multinational Corps-Iraq, said that since December 2004, US pilots have been shot at on average about 100 times a month and in most cases the rounds do little damage.