US President Barack Obama has told congressional leaders that he had the authority he needed to take action to destroy the Islamic State.

Mr Obama met with top Democratic and Republican leaders ahead of a speech tomorrow evening to lay out his plan to fight the group, also known as ISIL.

"The president told the leaders that he has the authority he needs to take action against ISIL in accordance with the mission he will lay out in his address tomorrow night," the White House said in a statement.

"He reiterated his belief that the nation is stronger and our efforts more effective when the president and Congress work together to combat a national security threat like ISIL."  

In a statement released after the meeting, Speaker of the House, Republican Congressman John Boehner said the President had laid out some of the ideas for combating IS that had he had already discussed publicly.

He said that he supported certain options such as using the US military to help train and provide an advisory role to the Iraqi security forces, and to help with killing the leadership of the IS organisation.

Earlier, US Secretary of State John Kerry hailed the new Iraqi cabinet as a "major milestone" for the country and "a cornerstone" in the fight against Islamic militants.

His comments come ahead of a trip to the Middle East to drum up support to defeat the Islamic State.

The top US diplomat vowed Washington would stand "shoulder to shoulder" with the Iraqis.

He said that a global coalition against IS would "be built to endure for months and perhaps even years to come."

Meanwhile, Obama administration officials will hold briefings this week and next for members of the US Congress as the president makes his case for an offensive against Islamic State militants, congressional aides said.

Administration officials will hold a briefing for all 435 members of the US House of Representatives on Thursday, a House aide said.

Senate aides said a similar session for the 100 members of the Senate is planned as early tomorrow.

The Senate Armed Services Committee announced yesterday that Secretary of Defense Chuck Hagel, and General Martin Dempsey, chairman of the Joint Chiefs of Staff, would testify on 16 September at a hearing on US policy toward Iraq and Syria and the threat posed by the Islamic State.

Mr Kerry is due to testify the same day before the House Foreign Affairs Committee.

No information Sotloff was 'sold' to IS - White House

Separately, a White House spokesman said the US has no information indicating murdered journalist Steven Sotloff was "sold" to IS militants by moderate Syrian opposition rebels.

Sotloff family spokesman Barak Barfi told CNN last night the family believed IS paid up to $50,000 to rebels who told the militant group the 31-year-old journalist had entered Syria.

"Based on the information that has been provided to me, I don't believe that is accurate," Josh Earnest told a news briefing.

He cited an FBI investigation of Mr Sotloff's death, including "how Mr Sotloff may have come into the hands of ISIL."

The militants released a video on 2 September showing the beheading of Mr Sotloff, who was kidnapped in Syria in August 2013.

Mr Barfi told CNN's "Anderson Cooper 360" that Mr Sotloff's family learned from unidentified "sources on the ground" that a member of a moderate Syrian rebel group contacted IS militants about the journalist.

Mr Barfi said the family was disappointed with the Obama administration's handling of the situation, but he did not elaborate and said the family would soon speak for itself.

President Obama is seeking to increase aid to moderate Syrian opposition groups who are fighting to oust President Bashar al-Assad and are also seen as a tool against IS.

The militants have seized territory in Syria and Iraq and declared an Islamic caliphate.

In a 19 August video showing the beheading of another US journalist, James Foley, the group said it was retaliating for US airstrikes on its insurgents in northern Iraq.

The United States resumed airstrikes in Iraq in August for the first time since the pullout of US troops in 2011.