WASHINGTON - US President Barack Obama is sending his defense chief next week to the Middle East, where he faces the unenviable job of reassuring allies such as Israel that a nuclear deal with Iran will not undermine America's commitment to their security.

It could be a very hard sell.

So far, the White House has only disclosed one stop on the trip - to Israel, where Prime Minister Benjamin Netanyahu condemned Tuesday's deal as "a stunning, historic mistake".

US defense officials told Reuters that Defense Secretary Ash Carter would travel elsewhere within the region but declined to offer details.

The agreement between Iran and six major world powers could transform the Middle East.