Attacks by Houthi rebels in Yemen have forced three quarters of U.S.-flagged ships to avoid the Red Sea and instead take the long and expensive detour around the southern tip of Africa, the U.S. national security advisor said Sunday.

"Seventy-five percent of our U.S. flag shipping now has to go around the southern coast of Africa rather than going through the Suez Canal," Mike Waltz told CBS's "Face the Nation."

He added: "The last time one of our destroyers went through the straits there, it was attacked 23 times."