WASHINGTON—U.S. Senator Chris Murphy (D-Conn.) released the following statement on the death of Kayla Mueller, a 26-year-old American who was held captive by Islamic State militants:

"My deepest condolences go out to Kayla Mueller's friends and family for their tragic loss. Kayla lived selflessly in the service others and her death is a heartbreaking reminder of the grave threat ISIL poses to our country. Far too many have been held captive and killed at the hands of these monsters, and I'll continue fighting for a tough and smart strategy for confronting and eliminating this enemy."