The United States is concerned about Iran providing weapons to Iraq militants and will take unilateral action when needed to deal with the threat, US Defence Secretary Leon Panetta said on Monday.

US officials have blamed Shi'ite militias armed by Iran for most of the recent attacks on US forces in Iraq. Fourteen US service members were killed in hostile incidents in June, the highest monthly toll in three years.

At least three more have been killed in July, including one on Sunday, the day Panetta arrived in Baghdad on his first trip to Iraq as defence secretary.     

Washington still has about 46,000 troops in Iraq more than eight years after the 2003 invasion that ousted Sunni dictator Saddam Hussein but is scheduled to withdraw its forces by year-end under a security pact between the two countries.

'We are very concerned about Iran and the weapons they are providing to extremists here in Iraq. And we're seeing the results of that,' Panetta said in an address to US troops in Baghdad.

'In June we lost a hell of a lot of Americans as a result of those attacks. And we cannot just simply stand back and allow this to continue to happen ...' 

Panetta said Washington's first effort would be to press the Iraqi government and military to go after groups responsible for the attacks. He was scheduled to meet Prime Minister Nuri Al-Maliki later on Monday.

'Secondly, to do what we have to do unilaterally, to be able to go after those threats as well, and we're doing that,' he said, referring to the right of U.S. forces to defend themselves on Iraqi soil.     

'And thirdly, to bring pressure on Iran to not engage in this kind of behaviour. Because, very frankly, they need to know that our first responsibility is to protect those that are defending our country. And that is something we are going to do.'     

US forces officially ended combat operations in Iraq last August and now operate largely in the background, training and assisting Iraqi police and soldiers against a weakened but still lethal insurgency that launches hundreds of attacks each month.

Hours after Panetta's arrival, militants fired three Katyusha rockets into Baghdad's heavily fortified Green Zone, home to the massive US embassy complex and Iraqi government buildings, according to an Iraqi Interior Ministry source. There were no immediate reports of casualties.     

US officials including Panetta have been pressing Baghdad to decide whether it wants US forces to stay beyond the year-end deadline. Maliki has said he will abide by a decision of the majority of Iraq's political leaders.

The Shi'ite, Sunni and Kurdish political blocs have given themselves another two weeks to decide their positions on the withdrawal. They are known to have widely disparate views on the possibility of some US soldiers staying.

Panetta said Iraq's foot-dragging was part of its democratic process even as he acknowledged 'sometimes it can be frustrating'. He asked out loud whether Iraq wanted the US military to stay on past the end of 2011, or whether they wanted to install a new defence minister.

Maliki did not name permanent security ministers when he installed his cabinet last December, holding the defence and interior ministries for himself.     

'But damnit make a decision! So it gets frustrating. But that's the nature of democracy ... that kind of debate, that kind of dialogue goes on,' Panetta said, adding 'it's healthy'. - Reuters