US Secretary of State John Kerry has said the international community will not sit and watch the Islamic State grow and identified Iraq as a key partner in the fight against the group.

"We all have an interest in supporting the new government of Iraq at this particular critical junction," Kerry said during a visit to Baghdad on Wednesday.

He said an international coalition to confront the Islamic State "will continue to grow and deepen in the days ahead.

"That is because the United States and the world will simply not stand by to watch as ISIL's evil spreads." Kerry said, using an alternative acronym for Islamic State.

Kerry's comments come as the US President Barack Obama is set to outline an expanded military and political effort to combat the Islamic State group in Syria and Iraq, and urge American legislators to quickly give him authority to arm Syrian opposition forces.

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Officials in his administration said Obama would press forward with other elements of his plan without authorisation from the US Congress.

The Islamic State group has taken control of large parts of Iraq and neighbouring Syria. The group's brutal campaign has included beheadings of rivals and killings of hundreds of members of Iraq's minorities.

The Associated Press news agency reported that Obama's new strategy against the Islamic State could include more air strikes in Iraq, where the US is already involved, and possibly in Syria.

Other elements of Obama's plan include increased support for the Iraqi security forces, as well as military and diplomatic commitments from partners in Europe, the Middle East and elsewhere.

After an hour-long discussion with congressional leaders on Tuesday, the White House said Obama told legislators that he had the authority he needed to take action against the Islamic State.

The speech will represent a chance for Obama to redress criticism that he has been slow to respond to the Islamic State challenge, amid fears fighters with Western passports could hit US targets.

Al Jazeera's Patty Culhane, reporting from Washington DC, said that Obama has the support of the American public, with 91 percent of them viewing the Islamic State as a threat to the US.

Obama started the work of creating an international coalition to take on the Islamic State at the NATO summit last week.

On Thursday, Kerry will head to Saudi Arabia to meet foreign ministers from the Arab states to continue efforts to form a coalition against the Islamic State group.

Source: Al Jazeera and agencies