Operators at the Leviathan natural gas field off the Israeli coast said Wednesday a Palestinian group canceled a $1.2 billion purchase contract.

Delek Group, which alongside Noble Energy holds an 85 percent stake in the Leviathan project, said it received a "conditioned cancellation notice of the natural gas supply agreement from the Leviathan project to Palestine Power Generation Co."

Leviathan is one of the largest regional gas fields, with an estimated 18 trillion cubic feet of reserves. Development was curtailed in late 2014 when the Israel Antitrust Authority said Delek Group and its partners at Noble Energy held a monopoly over all of the gas reservoirs off the nation's coast.

Both companies also control the nearby Tamar, estimated to hold as much as 10 trillion cubic feet of natural gas.

Delek in a statement said the conditioned cancellation from the Palestinian side was related to the lack of consent from Israeli antitrust authorities, the delay in approving the development plan and "the non-fulfillment of the conditions precedent set forth in the [2013] agreement."

Noble, which has headquarters in Houston, is the only U.S. partner working in Israeli waters. The company's chairman, Charles Davidson, said last year the anti-trust decision sets a "harmful precedent" for Israel.

The U.S. State Department facilitated talks last year that led to the signing of a regional deals for gas deliveries from Leviathan and Tamar.

The Palestinian power company in late 2013 signed a 20-year agreement to buy around 165 billion cubic feet of gas from Leviathan as soon as full-scale production begins. There was no public statement on the cancellation from the Palestinian group.