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The US is considering escalating its military campaign against the Islamic State of Iraq and the Levant (ISIL) group in Iraq and Syria, a US official said.

The new policy would mean additional air strikes and even "direct action" on the ground, US Defence Secretary Ashton Carter said on Tuesday, outlining a strategy shift that still needed approval from the president.

Testifying to politicians, Carter said US forces would not shy away from "direct action on the ground" if they see a chance to hit ISIL targets.

US President Barack Obama's administration has not committed ground forces to back opposition and Kurdish rebels fighting ISIL in Syria, but has 3,500 troops in Iraq.

These troops have a "train and advice" role to help Iraqi forces battling the group but were recently drawn into fighting in northern Iraq.

Last week, a US soldier died during a raid in which commandos and Kurdish Peshmerga stormed an ISIL-run jail in northern Iraq and freed 70 captives.

Afterwards, Carter said he expected "more of this kind of thing" and on Tuesday he told US senators the coalition would focus on the ISIL stronghold of Raqqa, in Syria.

"We expect to intensify our air campaign, including with additional US and coalition aircraft, to target ISIL with a higher and heavier rate of strikes," he said.

"This will include more strikes against ISIL high-value targets as our intelligence improves."

Carter described the strategy as centred on the "three Rs" - raids, Raqqa and Ramadi, the capital of Iraq's Anbar province, held by ISIL forces since May.

"We are willing to continue providing more enabling capabilities and fire support to help our Iraqi partners succeed," Carter told the Senate Armed Services Committee.

Iran to be invited

On the diplomatic side, the state department said it expected Damascus' key ally Iran to be invited to a new round of talks in Vienna this week on a political solution.

"An invitation to Iran to participate, I think Iranian leaders can take to mean that it's a genuine multilateral invitation," state department spokesman John Kirby said.


US says Iran to be invited to next round of Syria talks


US officials would not say which power would pass the invitation to Tehran and did not know if Iran would accept, but they said it would be welcome to attend.

Friday's talks in Vienna are seen as a way to end Syria's civil war by creating an interim unity government and paving the way for Syrian President Bashar al-Assad's exit.

On Tuesday, in confirming it expects Iran to be invited, Washington signalled that talks are progressing but risked angering Tehran's bitter foe Saudi Arabia.

Separately, Obama called Saudi leader King Salman.

The White House did not say whether Obama had tried to reassure Salman about Iran's participation.

Source: Al Jazeera and agencies