"We signed a heads of agreement (document) with Qatar Petroleum in January 2010 to progress the joint development of a world-scale petrochemical complex and we continue to work with Qatar Petroleum on the project," the spokesman said in an e-mailed statement to Reuters.

A heads of agreement is a non-binding document outlining the main issues relevant to a tentative partnership agreement.

Middle East Economic Digest magazine, citing unnamed sources close to the partners, said the pair ended plans for the new project after talks in June and July. Qatar Petroleum will now seek a new partner, MEED said.

Qatar Petroleum declined to comment.

"Specific details regarding the proposed project schedule, next steps and timing are considered confidential," the spokesman said.

Start-up of the plant, which has been delayed by three years, is slated to begin in 2015. Exxon and QP have been talking about the plant since signing an initial deal in 2005. A final deal was expected in 2006.

The complex is located in the industrial city of Ras Laffan and is estimated to cost $6 billion.

The complex includes a 1.6 million tons per year (tpy) steam cracker and associated units including two 650 tpy polyethylene plants and a 700 tpy ethylene glycol facility.