Britain's Home Secretary Theresa May vowed Monday that "the terrorists will not win" after paying tribute in Tunisia to the 38 people, mainly Britons, killed by a jihadist gunman.

"We will be united in working together to defeat them but united also in working to defend our values," May said at a joint press conference with her German, French and Tunisian counterparts after visiting the scene of the killings at a Tunisian beach resort.