U.S. Secretary of State John Kerry has said the United States will not be intimidated by Islamic State (IS) militants.
Kerry said the brutality of the group and its potential spread worldwide as a key reason, among many, that the United States must remain deeply engaged in the Mideast.
Left unchecked, Kerry said IS could grow worldwide.
Already, he said, the IS has seized more land and resources "than Al-Qaeda ever had on its best day of its existence."
Kerry was speaking in Washington on November 17, a day after the White House confirmed the death of U.S. aid worker Peter Kassig.
Islamic State militants released a video in which it claimed to have beheaded the American.
Kassig was captured by the extremists in eastern Syria in October 2013, while delivering relief supplies for the aid group he founded.