Obama still did not indicate a timeline for deciding on a strategy to go after the extremist group's operations in Syria.

"It'll take time to roll them back," said Obama at a Wednesday news conference during a visit to Europe.

Obama's remarks came after he said the United States had verified the authenticity of a video released Tuesday showing the beheading of freelance reporter Steven Sotloff, two weeks after journalist James Foley was similarly killed.

The American president further vowed that the U.S. would not forget the "terrible crime against these two fine young men."

"Our reach is long and justice will be served," Obama claimed.

"Our objective is to make sure that ISIL is not an ongoing threat to the region," he said, using an acronym for the militant group.

"And we can accomplish that. It's going to take some time and it's going to take some effort."

The 31-year-old Sotloff, who held dual Israeli and American citizenship and freelanced for Time and Foreign Policy magazines, vanished a year ago in Syria and was not seen again until he appeared in the video that showed Foley's beheading.

British Foreign Secretary Philip Hammond said Wednesday that the masked, British-accented ISIL terrorist appears to be the same person shown in the Foley footage.

In the video, the organization threatens to kill another hostage, this one identified as a British citizen, David Cawthorne Haines. It was not immediately clear who Haines was.

Meanwhile, US State Department spokeswoman Jen Psaki said Tuesday that it is believed that "a few" Americans are still being held by the Takfiri terror group.

Psaki would not elaborate, but one is a 26-year-old woman who was kidnapped while doing humanitarian aid work in Syria, according to a family representative who asked that the hostage not be identified out of fear for her safety.

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