EDGARTOWN Mass. (Reuters) - The White House on Friday said the United States stands ready to take additional action against Islamic State fighters who beheaded an American journalist and will not be restricted by the Iraq-Syria border.

U.S. airstrikes against Islamic State targets have been confined to Iraq thus far but U.S. officials have made clear they are considering taking the fight against the group into Syria, where it is based.

White House deputy national security adviser Ben Rhodes told reporters the United States stands ready to take action to protect American citizens. He said the group is more dangerous today than it was six months ago.

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U.S. officials this week disclosed an attempt that failed to rescue American hostages held by Islamic State militants. Rhodes said the United States has done everything it can to rescue American hostages held by the group and will keep trying.