WASHINGTON — President Barack Obama authorized additional military assistance for Iraq’s fight against advancing Islamist militants Thursday, but made clear that he will continue to hold back more substantive support, including U.S. airstrikes, until he sees a direct threat to U.S. personnel or a more inclusive and capable Iraqi government.

Obama said he would send up to 300 additional U.S. Special Operations troops to better assess the situation on the ground, where forces of the Islamic State of Iraq and Syria (ISIS) have moved ever nearer to Baghdad, and to determine “how we can best train, advise and support Iraqi security forces going forward.”

With the “situational awareness” provided by the advisers and with intelligence assets being increased in and around Iraq, Obama said, “we will be prepared to take targeted and precise military action if and when we determine that the situation on the ground requires it.”

But “American combat troops are not going to be fighting in Iraq again,” he said, a point he made repeatedly during remarks in the White House briefing room. “Ultimately, this is something that is going to have to be solved by Iraqis.”

The administration is straddling difficult politics in Iraq and at home, seeking to answer Republican critics such as House Speaker John Boehner of Ohio who claim that Obama is “taking a nap” while Iraq crumbles and to assure political supporters that he is not opening a new front in the Middle East.

In Iraq, U.S. diplomats are urgently pushing for a new government that can prevent a sectarian civil war in which Kurds move to protect their northern territory, estranged Sunnis join the militants, and the majority Shiites retreat into an Iran-backed fortress.

While Obama did not call directly for the departure of Prime Minister Nouri al-Maliki, he made clear that Maliki has not met the challenge of the current crisis.

“Right now is a moment where the fate of Iraq hangs in the balance,” he said. “And the test for all of them is going to be where they can overcome the mistrust, the deep sectarian divisions, in some cases just political opportunism and say, this is bigger than any one of us, and we’ve got to make sure that we do what’s right for the Iraqi people.”

The United States has backed Maliki’s leadership over the past eight years even as he shrugged off warnings about political inclusion and the resurgence of al-Qaida in Iraq, a Sunni extremist organization that was reborn as ISIS in neighboring Syria’s ongoing civil war.

Following elections in April, a new Iraqi parliament has until the middle of August to choose a government. U.S. diplomats, meeting this week with Maliki’s political rivals, have pressed them to move much more rapidly to form coalitions and establish a parliamentary majority. Those who say they will not support another government led by Maliki’s Shiite alliance have been asked to propose alternatives.

Deputy Prime Minister Saleh al-Mutlak, a Sunni, said he met with U.S. Ambassador Robert Stephen Beecroft and Deputy Assistant Secretary of State Brett McGurk on Wednesday. While “they didn’t say it directly,” Mutlak said, “between the lines they realize we can’t sit together with Maliki” in a future government.

On Wednesday evening, Vice President Joe Biden called Osama al-Nujaifi, the Sunni speaker of the previous parliament and an outspoken critic of Maliki. Biden, according to Nujaifi spokesman Dhafer al-Ani, “didn’t say he wanted Maliki out, but he said the United States didn’t support Maliki. We made clear our position that we would not be part of a government headed by Maliki.”

Forming a government after Iraq’s last election, in 2010, took more than eight months; the U.S. goal now is that it happen within weeks. “Our consistent message to everybody is to keep it moving forward,” said a senior administration official, one of several who spoke on the condition of anonymity to flesh out Obama’s announcement.

“In the meantime,” Obama said, “my job is to make sure that American personnel there are safe, that we are consulting with the Iraqi security forces, that we’re getting a better assessment of what’s on the ground and that we’re recognizing the dangers of ISIS over the long term and developing the kinds of comprehensive counterterrorism strategy that we’re going to need to deal with this issue.”

Obama said he was sending Secretary of State John Kerry to the region this weekend to consult with other governments in the Middle East and Europe. Kerry is also expected soon to travel to Iraq for a face-to-face meeting with Maliki.

U.S. officials discussed the Iraq situation this week with officials from Iran’s Shiite government on the sidelines of a meeting in Europe on the Iranian nuclear program. “Our view is that Iran can play a constructive role if it is helping to send the same message to the Iraqi government that we’re sending, which is that Iraq only holds together … if the interests of Sunni, Shia and Kurd are all respected,” Obama said.

“If Iran is coming in solely as an armed force on behalf of the Shia … then that probably worsens the situation,” he said.

In addition to increasing intelligence assets in Iraq — including manned and unmanned aerial reconnaissance — Obama has ordered up to 275 troops to bolster security for the U.S. Embassy and other American facilities in Baghdad. Those troops, and the new ones Obama announced Thursday, will effectively double the U.S. military presence in Iraq. About 600 military personnel assigned to the embassy have been handling U.S. military sales and other forms of cooperation since the last combat troops withdrew from Iraq at the end of 2011.

Some of the newly authorized forces, drawn from U.S. Central Command units already in the Middle East, will establish joint operations centers in Baghdad and northern Iraq to share intelligence and coordinate planning, including helping Iraqis target ISIS forces.

A second senior official said that “we will start with small teams of about a dozen each” positioned in “higher headquarters, perhaps down to the brigade level. … They are going to go in there and give us a little bit better sense of the state and cohesiveness of the Iraqi security forces and give us advice about the future role of any additional advisers.”

“We are going to start small,” the official said. But “the president made clear that unilateral military action and … discrete and targeted strikes remain a possibility … once we have better information” on the ground.

In the absence of any direct threat to U.S. personnel or facilities, Obama and other officials made clear that the United States will calibrate its assistance, including possible airstrikes, based on Iraq’s progress in forming a broad-based government.

Although the administration does not believe it needs formal congressional approval to respond to Iraqi requests for assistance, it has sought with telephone calls and other outreach to assure lawmakers that they will be consulted.

Senate Armed Services Committee Chairman Carl Levin, D-Mich., called the 300 advisers a “reasonable step” but said “we should be extremely cautious” about additional actions “such as airstrikes” without unified agreement from Iraqis.

Rep. Adam Schiff of California, the top Democrat on the House Armed Services Committee, warned of “mission creep” and said that while he supports the limited action announced Thursday, the United States “should not get involved in another land war in the Middle East. We have spent enough in both lives and money.”