U.S. Defense Secretary James Mattis gestures during a press briefing on the campaign to defeat ISIS at the Pentagon in Washington, U.S., May 19, 2017. REUTERS/Yuri Gripas

WASHINGTON (Reuters) - U.S. Defense Secretary Jim Mattis said on Friday the U.S.-led coalition was now encircling Islamic State fighters in their strongholds in a tactical shift before starting a military campaign to destroy them.

Also speaking at the Pentagon on Friday, the Chairman of the Joint Chiefs of Staff General Joseph Dunford, said strikes against Syrian government-backed fighters this week were a “force protection measure,” and would not happen again if U.S. forces are not threatened.