US Defence Secretary Leon Panetta arrived in Baghdad on Sunday to urge Iraqi leaders to act against Iran-backed Shiite militias, as another American soldier was killed in the south of the country. Panetta, who took office 10 days ago, flew in after visiting Afghanistan and was also to urge Iraqi leaders to decide soon on whether they want US troops beyond the scheduled pullout at the end of this year, a senior US defence official said. About 46,000 US troops remain in Iraq, down from a high of 170,000 after the 2003 US-led invasion. They are scheduled to leave in less than six months unless a deal is reached between Baghdad and Washington. \"If they are to make a proposal with regards to the continuing US presence there, they have to make a formal request that we would obviously consider,\" Panetta told reporters shortly after his arrival. He is due to meet President Jalal Talabani, Prime Minister Nuri al-Maliki and the president of Iraqi Kurdistan, Massud Barzani. \"The issues for Iraq are security there and what\'s being done, particularly to deal with the Iranian supply of weapons to militants in Iraq,\" Panetta said. Three American soldiers have been killed so far this month, after June was the deadliest month in three years for US troops, with 14 killed. A US military statement said a soldier was killed in southern Iraq on Sunday, but gave no other details. Asked about increased attacks on US forces by Shiite militants backed by Iran, Panetta expressed \"tremendous concern,\" and called on Iraq to do more to \"go after those extremists that are making use of these weapons\" supplied by Tehran. \"If we\'re all gonna be partners, they have a responsibility to protect against that kind of attack. It\'s in the interest of Iraq to provide for their own security,\" he said. Iran has denied US accusations that it was smuggling weapons to insurgents in two of its neighbours, Iraq and Afghanistan. Panetta said the United States was open to a request by Iraq on a troop extension. \"If they are to make a proposal with regards to the continuing US presence there, they have to make a formal request that we would obviously consider,\" Panetta told reporters. \"I think the secretary will convey to the Iraqis... that there\'s some urgency for them to make that request if they\'re going to make it,\" said a senior US official travelling with the defence secretary. Panetta is the latest top US official to arrive in Iraq, asking officials to accept a contingent of American troops beyond 2011. US diplomatic sources in Baghdad say there has been no talk on the possible number who could remain. A possible extension would be deeply unpopular among the public in Iraq, where many people look upon the American soldiers as \"occupiers.\" Talabani, a Kurd, said on Saturday that political parties would announce their decision in two weeks on whether they want some US forces to remain. Ali Mussawi, Maliki\'s media adviser, told AFP on Sunday that a decision within two weeks was unlikely. \"I believe that political leaders will not reach an agreement during the two-week deadline,\" he said, adding that leaders were too busy arguing over small issues instead of focusing on more important issues such as the future of American forces in Iraq. Some Kurdish officials have said they want US forces to stay beyond the deadline, but the powerful Shiite movement of Moqtada al-Sadr has threatened to resume armed struggle against American troops if they extend their stay. In a statement posted on his website on Sunday, Sadr said that due to internal issues he would not reactivate his powerful Mahdi Army even if US forces stayed, but added that the elite Promised Day Brigade would be at the forefront of the fight against American forces staying on. It is one of three militias that US military officials say receives weapons from Iran and has been behind attacks on US troops. Panetta said he would also press Iraqi leaders to speedily appoint defence and interior ministers, posts which remain vacant because of political bickering, despite the formation of a unity government last December.