Two American soldiers have been killed in central Iraq, the military said on Friday, reporting the first fatalities since June, the deadliest month for American forces in the country for three years.The deaths came as the top US military officer, Admiral Mike Mullen, confirmed Washington is negotiating to keep some troops in Iraq beyond a scheduled year-end pullout, and accused Iran of direct support for extremists he said were killing the soldiers. \"Two US service members were killed Thursday while conducting operations in central Iraq,\" said a brief statement by the military, which did not mention how or where they had died. In June, 14 American soldiers were killed in Iraq, most of theme in rocket attacks, making it the deadliest month since June 2008 when there were 23 fatalities. Thursday\'s deaths raise the full number of American military fatalities in Iraq since the 2003 US-led invasion to 4,471, according to an AFP count based on the website www.icasualties.org. About 46,000 US soldiers remain in Iraq, down from a high of 170,000 since the invasion, which toppled dictator Saddam Hussein. All are due to pull out by the end of this year according to a 2008 pact, but Admiral Mullen said on Thursday that Washington and Baghdad are negotiating to keep some US forces in the country beyond the December 31 deadline. \"The negotiations are ongoing and it\'s hard,\" Mullen told reporters at a Pentagon Press Association luncheon. His comments marked the first high-level confirmation from the US military that talks were underway on the politically charged subject, which faces some stiff opposition in Iraq. Mullen said the discussions were addressing both the size of a possible US military mission as well as the capabilities that Iraqi forces lacked. He would not speculate on the optimum number of troops that should remain, but said: \"It\'s what the Iraqi government and really the Iraqi people say is acceptable to them to provide for their own security.\" The US military chief also accused neighbouring Iran of directly supporting and supplying more lethal weapons to Shiite militants in Iraq who were killing US soldiers. \"Iran is very directly supporting extremist troops which are killing our troops,\" Mullen said. Iran has issued recent denials in response to US accusations it was smuggling weapons to insurgents in Iraq and Afghanistan.