The third-ranking official in the U.S. State Department has warned Iran about interfering in Iraq, again putting Iran on notice about its alleged support for Iraqi militants.

U.S. Undersecretary of State Nicholas Burns repeated previous claims that five Iranians detained in January in Iraq were suspected of passing on explosive technology to Shia militants.

"They're giving insurgent groups the technology to kill our soldiers," he told the BBC Wednesday."We have the absolute right to defend our soldiers."

Iran has protested the move. The five were in an Iranian diplomatic mission.

Iran, a Shia country, supports the Shia majority in Iraq. Shia militants are battling minority Sunni insurgents in Iraq, and both groups are suspected of attacking western soldiers in Iraq.

U.S. officials, right up to President George W. Bush, have recently told Iran to butt out of Iraq.

"Iran is seeking to destabilize Iraq, Lebanon, Israel and the moderate Palestinians," Burns said.

The U.S. government is preparing a report on Iran's support for militants in Iraq.

Earlier this week, Iran's ambassador to Baghdad, Hassan Kazemi Qomi, said Iran wants to help Iraq by opening a branch of the Iran National bank in Baghdad and training and supplying the Iraqi military.

Regional meeting to talk about Iraq's security

Iraq on Thursday confirmed that it had invited officials from its neighbours to a meeting in Baghdad to discuss the violence.

The meeting, set for March, is one in a series; the previous meeting was held in Iran last summer. 

Iraq has invited Iran and Syria, which the U.S. accuses of meddling in Iraq, as well as Bahrain, Egypt, Jordan, Kuwait, Saudi Arabia, Turkey, the Arab League, the Organization of the Islamic Conference and the United Nations, an Iraqi official told the Associated Press.

A U.S. spokesman endorsed the idea of the meeting on Wednesday.

With files from the Associated Press