Iraq crisis: President Obama can 'bypass Congress'
US President Barack Obama has told Congressional leaders he does not need lawmakers' approval for any action in Iraq, the top Senate Republican says.
Senator Mitch McConnell was speaking after a meeting between the president and senior members of Congress.
Iraq has asked for US air strikes against advancing jihadist militants, who have seized key cities and towns.
But correspondents say any decision on military support from Washington could hinge on political changes in Iraq.
US Vice-President Joe Biden discussed possible "additional measures" that could help "roll back the terrorists' advances" with Iraqi Prime Minister Nouri Maliki on Wednesday, but also the need for national unity.
The Obama administration has shown signs of frustration with Mr Maliki - a Shia Muslim who has long been accused of discriminating against the Sunni Arab minority community and monopolising power.
Defence Secretary Chuck Hagel told a congressional hearing: "This current government in Iraq has never fulfilled the commitments it made to bring a unity government together with the Sunnis, the Kurds, and the Shia."
Mr Obama met Congressional leaders at the White House on Wednesday to discuss the US response to recent advances by the Islamic State in Iraq and the Levant (ISIS).
Speaking afterwards, Mr McConnell said the president had "indicated he didn't feel he had any need for authority from us for steps that he might take".
Correspondents say the White House has so far avoided the thorny question as to whether it needs Congressional authority for any military action in Iraq.
Experts say Mr Obama has several options, including citing the Authorisation for the Use of Military Force (AUMF) against al-Qaeda and its associated forces passed by Congress in 2001; the 2002 AUMF that led to the invasion of Iraq; and his own powers as commander-in-chief.
Last year, the president abandoned plans for punitive military strikes in Syria following a deadly chemical weapons attack once it became clear that Congress would not give its backing.
Administration officials say the president may be able to act unilaterally in Iraq because its government has requested US air strikes against ISIS, which seized the second city of Mosul last week and is advancing southwards towards Baghdad.
ISIS and their Sunni Arab allies are reported to be advancing in Diyala and Salahuddin provinces after they overran Iraq's second city, Mosul, last week.
Analysis: Nick Bryant, BBC News, Washington
The White House has been reiterating its view that the Iraq crisis is not primarily a military challenge but instead requires a political solution.
To that end, Vice-President Joe Biden telephoned Iraqi Prime minister Nouri Maliki, one of his main Sunni rivals and also a Kurdish leader to press for a new government of national unity. Republican Senator John McCain has gone further - and called on Mr Maliki to step down.
Some senior Democrats have echoed that call. The Wall Street Journal is reporting that the Obama administration would also prefer to see the removal of a prime minister who it believes has heightened sectarian tensions and helped give rise to ISIS.
Unquestionably, the White House is intensifying its efforts to make the new Iraqi government look more like Iraq.
They have also launched an assault on Iraq's biggest oil refinery at Baiji, north of Baghdad.
The administration has not officially responded to Iraq's request for air support in its response to the offensive.
BBC security correspondent Frank Gardner says Mr Obama has a wide range of options, from air strikes to providing extra training, but that the US will - as a minimum - send in surveillance drones.
Ahead of Wednesday's meeting, Senate leader Harry Reid, a Democrat, said he did not "support in any way" getting American troops involved in Iraq's "civil war".
'Danger to unity'
Hundreds of people have been killed since the start of the militant offensive, many of them believed to be captured soldiers publicly shot by ISIS-led firing squads.
In an interview with the BBC, the representative of Grand Ayatollah Ali al-Sistani, the most senior Shia cleric in Iraq, warned against "a real danger which threatens Iraq and its unity".
Speaking to BBC world affairs editor John Simpson, Sheikh Abdul Mahdi Karbalai said the response should be "a stance which is adopted by people from all sects".
Iranian President Hassan Rouhani said Tehran would not "spare any effort" to defend Shia holy shrines in Iraq against "mercenaries, murderers and terrorists".
The representative of the United Nations Children's Fund (Unicef) in Iraq told the BBC that the situation facing the at least 400,000 people displaced by the fighting in the north was "dire".
Dr Marzio Babile added that he was extremely concerned about minorities,
"We need to protect children who are Christian, Turkmen or Assyrian, belonging to different ethnic groups, who are at extraordinary high risk of violence and, obviously, retaliation."
ISIS in Iraq
ISIS grew out of an al-Qaeda-linked organisation in Iraq
- Estimated 10,000 fighters in Iraq and Syria
- Joined in its offensives by other Sunni militant groups, including Saddam-era officers and soldiers, and disaffected Sunni tribal fighters
- Exploits standoff between Iraqi government and the minority Sunni Arab community, which complains that Shia Prime Minister Nouri Maliki is monopolising power
- ISIS led by Abu Bakr al-Baghdadi, an obscure figure regarded as a battlefield commander and tactician