As the first American defense secretary to visit Iraq since the U.S. officially ended its long war three years ago, Chuck Hagel's message to Iraqi leaders was plain: U.S. military power didn't solve Iraq's problems last time, nor will it now.

"As Iraqi leaders and the people of Iraq know, only they can bring lasting peace to their country — if they are resolved to do this," Hagel told reporters Tuesday after meeting Prime Minister Haider al-Abadi and other top Iraqi officials.

Hagel offered assurances that Washington is committed to helping Iraq regain the territory it lost to Islamic State fighters this year, and he emphasized the importance of building a durable international coalition to combat the extremist group. But equally important was his insistence that no amount of outside assistance can substitute for Iraqi will.

He acknowledged that al-Abadi had asked him for more American air power and more U.S. heavy weaponry. "We need that," the prime minister could be heard telling Hagel as they began their meeting in al-Abadi's office. Asked by reporters later how he had responded, Hagel pointedly declined to say whether he agreed with al-Abadi.

U.S. warplanes have been attacking Islamic State targets across much of northern and western Iraq since August. In the months ahead, the Pentagon hopes to increasingly use air power in conjunction with Iraqi ground counteroffensives to retake territory. But Hagel's remarks seemed intended to encourage the idea that the Iraqis' main focus should be on strengthening their own forces rather than appealing to Washington for a silver-bullet solution through U.S. firepower.

Hagel, who resigned under pressure barely two weeks ago, stuck to the Obama administration's insistence that Iraq's problems ultimately are rooted in political weakness that created the conditions for the Iraqi army's collapse last June, when Islamic State fighters swept across northern Iraq, captured the city of Mosul and stirred fear in Baghdad. In recent weeks the Iraqi security forces have staged a modest rebound, essentially halting further IS advances.

"For these gains to be sustainable, the Iraqi government must continue to build an inclusive government that represents all its people — a government that all of the Iraqi people can have confidence in and trust," Hagel said.

While it encourages the Iraqi government to pull together, the U.S. is working to build an international coalition that would help rebuild the Iraqi army. Four sites for the retraining of Iraqi forces are to be set up, with trainers from the U.S. and other countries.

U.S. Army Lt. Gen. James Terry, the top officer overseeing the U.S. military effort in Iraq and Syria, said Monday that about 1,500 trainers have been pledged by a variety of countries in Europe and the Middle East, with details yet to be worked out.

James Stavridis, a retired Navy admiral and dean of the Fletcher School of Law and Diplomacy at Tufts University, said Tuesday he believes training and advising Iraqi troops ultimately will require 8,000 to 10,000 troops. He called the provision of 1,500 trainers from allied countries the most encouraging new development in the fight against IS.

"Heavy weapons and more airpower would help, but building a true coalition with international partners is more important," Stavridis, a former commander of NATO forces in Europe, said in an email exchange. "This battle will be won or lost by allied boots on the ground, doing the hard work of training, advising and inspiring a shaky Iraqi army, not through throwing high-caliber weapons systems at the problem."

Hagel was the first Pentagon chief to visit Iraq since Leon Panetta attended a ceremony in Baghdad in December 2011 that marked the end of the U.S. war and the final withdrawal of U.S. troops more than eight years after the U.S. invaded to topple President Saddam Hussein. The U.S. left believing it had put the Iraqi army on a solid footing, but it unraveled over time.

Starting with the introduction last spring of small teams of U.S. military personnel to advise the Iraqi military and assess the condition of its army, the size and role of the American military presence has grown. There are now about 1,650 U.S. troops in Iraq.

Although President Barack Obama has stuck to his pledge not to send combat forces to fight IS in Iraq, he is likely to face decisions next year about authorizing riskier work for U.S. military advisers. That is because the Iraqi army is aiming to launch a counteroffensive to retake Mosul, the largest city in northern Iraq. When that happens, U.S. commanders may want to put U.S. advisers in the field with the Iraqis to help coordinate air and ground operations.

Hagel suggested Tuesday in Baghdad that such a moment may not be far off.

"Retaking Mosul is part of the plan," he told a news conference. "We're working with the Iraqis and their senior leaders on preparations."

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