WASHINGTON - Iran's missile attack on Wednesday had been intended to kill US personnel at Iraq's al-Asad airbase, the top US military officer said, in remarks that suggested that Tehran was, and perhaps still is, willing to risk major US retaliation.Army General Mark Milley, the chairman of the Joint Chiefs of Staff, was not ready to say whether Iran was done after its unprecedented attack on two Iraqi bases that host troops from the United States, Canada, Denmark, the United Kingdom and other nations. Asked if perhaps Iran would see this as an incomplete mission, given the lack of US fatalities, Milley said: "I think it's perhaps too early to tell."Milley said he and others in the military "fully expect" Shia militia groups in Iraq, backed by Iran, to carry out attacks against US and US-led forces in Iraq and Syria: "That's a very real possibility."His remarks came hours after President Donald Trump on Wednesday suggested Iran was "standing down" after it fired missiles at US forces in Iraq overnight, as both sides appeared to be looking to defuse a crisis over the US killing of an Iranian general.Iranian Foreign Minister Mohammad Javad Zarif had said the strikes "concluded" Tehran's response to the US killing of Iranian commander Qasem Soleimani on Jan. 3.Iranian Supreme Leader Ayatollah Ali Khamenei, addressing a gathering of Iranians chanting "Death to America," said the missile attacks were a "slap on the face" of the United States and said US troops should leave the region.Trump said the United States did not necessarily have to respond militarily to Iran's attack.US Defense Secretary Mark Esper, standing alongside Milley, cautioned that the US military remained "poised and ready."Milley and Esper offered the most detail to date about the Iranian missile attack overnight, telling reporters at the Pentagon that Iran fired 16 short-range ballistic missiles from at least three locations inside Iran.At least 11 of them hit al-Asad, while at least one other missile hit a facility in Erbil, Iraq. The others failed in flight. Esper said targets hit included tents, a helicopter and a parking lot and there was no major damage.MISSILES WITH SIGNIFICANT POWERMilley noted the missiles had 1,000 to 2,000-pound warheads on them, each with significant explosive power and "kill radius.""I believe, based on what I saw and what I know, is that (the strikes) were intended to cause structural damage, destroy vehicles and equipment and aircraft and to kill personnel. That's my own personal assessment," Milley told reporters."But the analytics is in the hands of professional intelligence analysts. So they're looking at that."Milley and Esper said actions taken by military personnel safeguarded lives, as well as early warning from US military systems that detect such missile activity.Milley noted that bases like al-Asad have scatter plans, bunkers and protective gear to help protect forces that come under attack.Esper and Milley said they were unaware of any heads-up from Iraq about the coming attack, after Baghdad said it was notified by Tehran of the strike.