Pending an agreement with Jordan or another nation to host the effort, the training was "likely" to go ahead as both Baghdad and Washington supported the idea, said the official, who spoke on condition of anonymity.
However, Pentagon officials are not contemplating sending an American team of military instructors into Iraq, partly because it would require negotiating a legal agreement with Baghdad that proved elusive in the past.
Such a move also could spark political rancour in Washington that would revive old wounds over the controversial US-led war in Iraq.
He said a possible counter-terrorism training effort was under consideration and that the Pentagon planned to send weapons and ammunition at the request of the Iraqi government.
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Iraqi Prime Minister Nuri al-Maliki "is looking for essentially small arms and ammunition, stuff that can help him right now" in the fight against Islamist extremists, Warren said.
The United States was preparing to ship "several thousand" M-16 and M-4 assault rifles as well as ammunition, the defence official said.
The United States led an invasion of Iraq in 2003, toppling Saddam Hussein. American troops withdrew from the country in 2011 after failing to reach a deal with Baghdad providing legal safeguards for US forces.
Less than 300 US troops are now stationed in Iraq, with a contingent of Marines guarding the American embassy and more than 100 service members overseeing military assistance.
In an interview published yesterday, Maliki had said his government was benefiting from intelligence provided by Washington and had asked for weapons and counter-terrorism training.
Asked if US trainers would come to Iraq, the prime minister had said, "Yes, bringing Americans to Iraq, or Iraqi soldiers could go to Jordan and train.