The United States is preparing to send new aid to Iraq to help counter a violent insurgency that is threatening to take over the nation's north, officials said.
But the Obama administration offered only tepid support for Iraq's beleaguered prime minister, Nouri al-Maliki, while US representatives openly questioned whether he should remain in power.
With no obvious replacement for Mr al-Maliki - and no apparent intent on his part to step down - Washington is largely resigned to continue working with his Shia-led government that has targeted Sunni political opponents and, in turn, has inflamed sectarian tensions across Iraq.
Senator Bob Corker, the top Republican on the Senate Foreign Relations Committee, said of the Iraqi leader: "He's obviously not been a good prime minister.
"He has not done a good job of reaching out to the Sunni population, which has caused them to be more receptive to al-Qaida efforts."
The panel's chairman, Senator Bob Menendez, a Democrat, noted only lukewarm support for Mr al-Maliki, both in Iraq and among US officials. "I don't know whether or not he will actually be the prime minister again," Mr Menendez said.
"I guess by many accounts, he may very well ultimately put (together) the coalition necessary to do that."
Insurgents with the Islamic State of Iraq and the Levant, which is inspired by al-Qaida, overran the northern Iraqi town of Tikrit on Wednesday, a day after seizing Mosul, the nation's second-largest city.
The insurgent network has controlled the western city of Fallujah since the start of this year, and is fighting to take over Beiji, a key northern oil refinery town.
The rampage has raised new doubts about Mr al-Maliki's ability to protect Iraq in areas that were mostly calm when US troops withdrew from the country less than three years ago.
Since then, violence has returned to levels comparable to the darkest days of sectarian fighting nearly a decade ago when the country teetered on the brink of civil war.
Mr Al-Maliki and other Iraqi leaders have pleaded with the Obama administration for more than a year for additional help to combat the growing insurgency, which has been fuelled by the unrelenting civil war in neighbouring Syria.
Northern Iraq has become a waystation for insurgents who routinely travel between the two countries and are seeding the Syrian war's violence in Baghdad and beyond.
State Department spokeswoman Jen Psaki said it is expected that the US will give Iraq new assistance to combat insurgents but declined to describe it.
Beyond the missiles, tanks, fighter jets and ammunition that the US has already either given or plans to send to Iraq, Baghdad has sought American surveillance drones to root out insurgents.
"The situation is certainly very grave on the ground," Ms Psaki said. She added that the US is encouraged by Baghdad's recent promise for a national unity effort but "there's more that prime minister Maliki can do."
"We agree that all Iraqi leaders, including prime minister Maliki, can do more to address unresolved issues there, to better meet the needs of the Iraqi people," Ms Psaki said.
US support for Mr al-Maliki has waxed and waned since 2010, when he hung onto power though backroom deal-making after his State of Law party fell short of winning national elections.
In 2011, days after the US troop withdrawal, Mr al-Maliki's government began a campaign of persecuting his longtime Sunni political opponents which, in turn, fuelled Sunni anger in the Shia-majority country.
Mr al-Maliki's party won the most seats in the most recent elections held in April, but it failed to capture a clear majority. That spawned a rash of political bargaining in Baghdad as officials built a new power-sharing government.
If he remains in power, it's far from certain that Mr al-Maliki will reverse his heavy-handed tactics after eight years in control, and Washington would most likely be happy with a change in leadership.
However, a senior Iraqi official said al-Maliki has no intention of stepping down, despite demands from Sunni and Shiite rivals to give up his post.
Mr al-Maliki's opponents have for years been unable or unwilling to work together to unseat the prime minister and, in the meantime, there are few people in Iraq's current government who could replace him.