The United States says Israel and mediators have reached an "understanding" about the outline of a truce in the Gaza Strip in exchange for the release of hostages held by the Islamic group Hamas.

White House National Security Advisor Jake Sullivan made the remark in a CNN interview on Sunday. The US, Egypt and Qatar are mediating negotiations in Paris over the Israel-Hamas conflict.

Sullivan said Israel and the mediators came to an understanding "about what the basic contours of a hostage deal for temporary ceasefire would look like."

He declined to go into specifics on the grounds that negotiations are still underway to hammer out the details.

Sullivan said "we will have to wait and see" if there is "actually a firm and final agreement." He added that ultimately Hamas "will have to agree to release the hostages."