Memorial service held for IS victim Steven Sotloff

Nearly 1,000 mourners including relatives, friends and politicians, have attended a memorial service in Florida for US journalist Steven Sotloff, who was killed by IS militants.

The Islamic State released a video on Tuesday showing the murder of Mr Sotloff.

He is the second American journalist to be beheaded in two weeks over the group's confrontation with the US over air strikes in Iraq and its foreign policy.

Footage of James Foley being beheaded on August 19 shocked the world.

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Video means it may be impossible for US not to act

By ITV News Washington Correspondent Robert Moore

With an American citizen butchered on camera for the world to see and President Obama personally being taunted, I think it may be politically, even emotionally, impossible for the US not act more aggressively against the Islamic State.

Given that the IS effectively no longer acknowledges the Iraqi-Syrian border, one option is for US warplanes to strike now deep inside Syria. But there are clearly some very major problems with that. Any such intervention in Syria would be be seen as siding to strengthen President Assad, and strengthening in many ways Shiite forces.

So that would have unforeseen consequences. In addition, any realistically major campaign against the Islamic State is going to need the deployment of US Special Forces, and that in turn would break this President's single most significant pledge to the American people - that there would not be boots on the ground. I think for the President and for his US security team, this remains an almost impossible dilemma.

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