DUBAI (Reuters) - Total CEO Patrick Pouyanne said on Sunday that the French oil and gas company would seek a waiver to continue the development of an Iranian gas field should the United States decide to reimpose sanctions.

Last July, Total became the first Western energy firm to sign a deal with Iran since the easing of international sanctions in 2015, agreeing to develop Phase 11 of the South Pars offshore gas field with a total investment of $5 billion (3.59 billion pounds).

Speaking in an interview with The National newspaper while on a visit to the United Arab Emirates, Pouyanne said Total's plans should be allowed to proceed because its agreement with Iran was awarded at a time when sanctions were not in place.

"If the U.S. decides to put back the sanctions, we have to look at what the consequences are ... and then we will see, either Donald Trump decides to maintain the waivers and we will move on with the project," he was quoted as saying.

"If the U.S. decides not to sign the waiver ... we will ask for a waiver from the U.S. authorities."

U.S. President Trump has expressed frustration at a landmark agreement between world powers and Iran over Tehran's disputed nuclear programme and cited Tehran's ballistic missiles and role in Syria's war as reasons the deal could be nullified.

(Reporting By Noah Browning; Editing by Susan Fenton)