Iraqi Shiite explosive and assassination teams are being trained in at least four locations in Iran by Tehran's elite Quds force and Lebanese Hezbollah, according to intelligence gleaned from captured militia fighters and other sources in Iraq.

A senior U.S. military intelligence officer in Baghdad also said the fighters planned to return to Iraq in the next few months to kill specific Iraqi officials as well as U.S. and Iraqi forces.

The intelligence officer described the information Thursday in an interview with The Associated Press. He spoke on condition of anonymity because of the sensitivity of the intelligence information.

The officer on Wednesday provided Iraq's national security adviser with several lists of the assassination teams' expected targets. The country's intelligence service is preparing operations to determine where and when the specially trained fighters will enter Iraq and will provide an assessment to Prime Minister Nouri al-Maliki, the intelligence officer said.

Iran, Hezbollah's mentor, denies giving any support to Shiite extremists in Iraq.

The U.S. official disclosed the information in an attempt to create political pressure on Iran to suspend the training and prevent the militia fighters from returning to Iraq.

The U.S. military also wants the Iraqi government to take steps to protect the targets. "Wanted" posters picturing men believed to be heading the special groups are being posted around Baghdad, the military officer said.

The fighters are expected to return to Iraq between now and October, but the officer said there's no intelligence suggesting they are actually in Iraq yet.

Many of the fighters fled to Iran this spring after Iraqi government forces cracked down first on militia sanctuaries in Basra and Sadr City in Baghdad, then Amarah, and now in Diyala province, the military officer said.

One of the reasons the U.S. believes the special groups moved out during that period is the sharp decline in the number of deadly roadside bombs using explosively formed penetrators.

In March, there were 55 such attacks. By July, that number had dropped to around 18, the officer said. U.S. intelligence believes those sophisticated bombs can be traced back to Iran.

The officer said training is going on in at least four locations in Iran: Qom, Tehran, Ahvaz and Mashhad.

Iran's President Mahmoud Ahmadinejad said Friday that regional nations should fill the security vacuum when U.S. troops withdraw from Iraq but said there was no prospect of sending in Iranian forces.

The United States and Iraq have worked on a deal this year to try to ensure Iraqi security but have disagreed on timing for American troops to withdraw. Iraq has insisted on a timetable but President Bush has refused to accept one.

"The United States will soon leave the region, then regional countries should fill the security vacuum; there is no need for interference of other countries," Ahmadinejad said on the final day of a two-day visit to Istanbul, Turkey's financial and cultural center.

U.S. and Iraqi negotiators missed a July 31 target date for completing a security deal amid disagreement over U.S. troop withdrawals. Iraq's Shiite-led government believes a schedule is essential to win approval for a security deal in parliament.

Ahmadinejad said Iraq's "stability and territorial integrity," was important for Iran, a position backed by his Turkish hosts. "We all have to protect the state of Iraq."

The elite Quds Force is a branch of Iran's Revolutionary Guard. The Islamic militant group Hezbollah, based in Lebanon, is believed to receive weapons from Syria and Iran.

The number of "special group criminals" — the U.S. name for Iraqi fighters sponsored by Iran — is unknown but is estimated to be in the hundreds and possibly more than 1,000.

According to the officer, the training camps are operating under the direction of Quds force commander, Brig. Gen. Ghassem Soleimani, with the knowledge and approval of Iran's supreme leader, Ayatollah Ali Khamenei.

The training includes how to conduct reconnaissance to pinpoint targets, small arms and weapons training, small unit tactics, and terrorist cell operations and communications.

They are also learning how to use explosively formed penetrator bombs and other improvised explosive devices and rocket propelled grenades, including the RPG-29, a signature weapon of Lebanese Hezbollah and the Quds force.

Lebanese Hezbollah conducts much of the training in the camps because its members speak Arabic, the dominant language in Iraq.

The U.S. officer said there were no confirmed reports of Lebanese Hezbollah members crossing into Iraq.

That conflicts with what Iraqi Shiite lawmakers and a top Army officer told The AP last month: Hezbollah trainers were running training camps in southern Iraq until April, when they were pushed into Iran by the Iraqi crackdown.

The trainees in the Iranian camps include three Iraqis already wanted by the Iraqi government for terrorist attacks: Haji Mahdi, Haji Thamir, and Baqir al Sa'idi, the officer said. He identified two Iraqi Shiite militia groups in Iran by name: "The League of the Righteous," or "Asaib al Haq," and the "Kataib al Hezbollah."

The "special group criminals" are offshoots of cleric Muqtada al-Sadr's Jaysh al-Mahdi militia. They spun off their own groups after al-Sadr declared a cease-fire with the Iraqi government in August 2007 and are not thought to be under his control now.