Qatar signed a deal with Royal Dutch Shell on Sunday to develop a $6.4 billion (4.1 billion pounds) petrochemicals complex in the Ras Laffan industrial city in the Gulf Arab state.

Qatar's energy minister, Mohammed al-Sada, and Shell chief executive Peter Voser signed the heads of agreement in Doha.

We estimate the cost to be $6.4 billion but at this stage one should be cautious, Sada said.

Asked whether the agreement replaced a similar one signed with U.S. group Exxon Mobil , Sada said: No, this is not a replacement. This is a continuation of our strategy. There will be other petrochemical plants in the pipeline.

While industry sources said last year they believed Exxon had pulled out of the agreement, chief executive Rex Tillerson denied that and told reporters the company was waiting for Qatar to make its decision.

Qatar is the world's largest exporter of liquefied natural gas (LNG), gas chilled for export by ship.

(Reporting by Regan E. Doherty; Editing by Firouz Sedarat and Dan Lalor)