Iran accused the United States Sunday of not taking the threat from Islamic State militants in Iraq and Syria seriously, and charged that US aid had previously helped the jihadists.

Foreign Minister Mohammad Javad Zarif levelled the accusations despite an expanding US air campaign in Iraq since August 8 that provided key support in relieving a jihadist siege of a Shiite Turkmen town north of Baghdad late last month.

Iran and the United States have a shared opposition to IS, which controls a swathe of both Iraq and neighbouring Syria, but both governments deny cooperating militarily against the jihadists.

"There is still no serious understanding about the threat and they (the United States) have as yet taken no serious action," Zarif was quoted as saying by Iran's Mehr news agency.

"They have helped (IS) in Syria in different ways," he added, alluding to support that the United States has provided to some rebel groups fighting President Bashar al-Assad's forces.

Iran has been Assad's main ally since a revolt against his rule erupted in 2011, rapidly spiralling into a civil war in which at least 191,000 people have been killed, according to the United Nations.

Shiite Iran has also provided military advisers to the Shiite-led government in Baghdad to assist its efforts to win back territory north and west of the capital that it lost to a lightning offensive spearheaded by the jihadists in June.

On Sunday, the United States expanded its month-long air campaign in Iraq, launching strikes against IS fighters in the country's Sunni Arab heartland around a strategic dam on the Euphrates River. IS has repeatedly tried to capture the dam from government troops and their Sunni militia allies.

Although Tehran and Washington have denied cooperation in Iraq, State Department spokeswoman Marie Harf said Friday that the US was "open to engaging" with Iran, as it has on select issues in the past, notably on Afghanistan in late 2001.

"But we will not be coordinating our action together," she added.

Despite his criticism of Washington, Zarif said Tehran believed in the need for international cooperation to tackle the IS threat.

"We were aware of this danger from the beginning and we helped the Iraqi people, whether Shiite, Sunni or Kurdish and we managed to prevent this threat from spreading," he said.

"This danger threatens the entire region and requires international cooperation."

Kerry discusses IS with Arab League chief
Washington (AFP) Sept 07, 2014 - Secretary of State John Kerry discussed Saturday the Islamic State threat with the head of the Arab League, ahead of the group's next round of discussions.

The Arab League is due to hold a ministerial meeting in Cairo on Sunday to address fast-moving changes in the region.

Kerry and Arab League chief Nabil al-Arabi "discussed the need for the Arab League and its members to take a strong position in the coalition that is developing against ISIL," a senior State Department official said, using one of the acronyms by which the Islamic State is known.

They also spoke of "the importance of decisive action to stop the flow of foreign fighters, counter ISIL's financing and combat its incitement," the official added.

Both men agreed that Iraq is on the frontline in the struggle against IS "and that Iraq, the United States, the region, and the international community must stand together to assist Iraq in facing this threat," the official said.

Iraq earlier welcomed US President Barack Obama's plan for an international coalition against jihadists as a "strong message of support," after repeatedly calling for aid against the militants.

Obama outlined the plan at a NATO summit Friday for a broad coalition to defeat IS, which led an offensive that overran chunks of five Iraqi provinces in June and also holds significant territory in neighboring Syria.

Obama anti-jihadist plan 'strong message of support': Iraq FM
Baghdad (AFP) Sept 06, 2014 - US President Barack Obama's plan for an international anti-jihadist coalition is a "strong message of support" for Baghdad and its fight against militants, Iraqi Foreign Minister Hoshyar Zebari said Saturday.

"We welcome that, and we have repeatedly called on our international partners for help and support because this threat is a very deadly threat... not only to the people of Iraq or the region, but to Europe, to America, to NATO," Zebari told AFP.

"This is basically our fight... but we need the support -- our capacity is limited, and we need the support to enhance our capacity," he said.

"Nobody's thinking of any ground troops at this stage -- they are calling for air support, for tactical support, for arming the forces on the ground, like the (Kurdish) peshmerga, the Iraqi security forces, and also to provide... intelligence, reconnaissance," he added.

Obama outlined plans at a NATO summit on Friday for a broad coalition to defeat the Islamic State (IS) jihadist group, which led an offensive that overran chunks of five Iraqi provinces in June, and also holds significant territory in neighbouring Syria.

The initial militant drive swept Iraqi security forces aside, but the federal government won its first major victories of the conflict in recent days, breaking a months-long siege of one town and retaking other territory from the militants.