Amid reports that a British national may be the masked terrorist shown on a video of the beheading of U.S. journalist James Foley by the Islamic State, British Prime Minister David Cameron announced Wednesday that he's cutting his vacation short and returning to London to deal with the threat.

Meanwhile, President Obama, who returned to Martha's Vineyard on Tuesday to resume his vacation after two days in Washington, planned to deliver a public statement from there.

The video, released earlier Tuesday, is putting new pressure on Obama to toughen his approach to the Islamist extremist group. So far, the president has limited U.S. efforts to airstrikes designed to help Iraqi and Kurdish forces roll back some of the group's gains in Iraq to buy time for a new, more inclusive government to form in Baghdad that may provide a more forceful response.

It remains to be seen whether Obama's hope to avoid "mission creep" in Iraq can be sustained under increased pressure from lawmakers and citizens concerned that the Islamic State has grown too strong as the U.S. has sat on the sidelines without a workable plan to defeat it.