"The international agreement for the development of phase 11 of South Pars will be signed on Monday in the presence of the oil ministry and managers of Total, the Chinese company CNPC and Iranian company Petropars," a ministry spokesman told AFP.

Total signed a preliminary deal with Iran in November, taking a 50.1 percent stake in the $4.8 billion (4.2 billion euro) project.

China National Petroleum Corporation (CNPC) will own 30 percent and Petropars 19.9 percent.

Total will put in an initial $1 billion for the first stage of the 20-year project.

The gas produced will "feed into the domestic Iranian market starting from 2021," a Total spokesman told AFP in Paris.

He said the company would "implement the project with the strictest respect for national and international law".

The contract was initially due to be signed in early 2017, but CEO Patrick Pouyanne said in February that Total would wait to see whether the US adminstration of President Donald Trump reimposed sanctions on Iran.

Trump threatened during his campaign to tear up the landmark accord between Iran and six world powers that came into force in January 2016 and eased sanctions in exchange for curbs to Tehran's nuclear programme.

His administration has taken a tough line on Iran and imposed fresh sanctions related to its ballistic missile programme and military activities in the region.

But the White House has kept the nuclear deal alive, continuing to waive the relevant sanctions every few months as required under the agreement.

It is partway through a 90-day review on whether to uphold the deal, although any move to abandon it would be strongly opposed by the other signatories -- Britain, France, Germany, China and Russia.