Asked whether ConocoPhillips would sell its stake in the consortium, Kazakh Oil and Gas Minister Sauat Mynbayev told reporters: "They have informed that they have the intention of selling."

The U.S. oil major owns an 8.4 percent stake in the field.

Lyazzat Kiinov, the head of Kazakh state oil company KazMunaiGas, said the firm was "displaying interest" in buying the stake of ConocoPhillips. He did not elaborate.

A more assertive Kazakhstan, Central Asia's largest economy and second only to Russia among former Soviet oil producers, has sought in recent years to revise deals struck with foreign energy firms in lean post-Soviet years.

The country, four times the size of Texas and home to three percent of the world's recoverable oil reserves, has also moved to exert greater management control and secure bigger revenues from foreign-owned oil and gas developments.

KazMunaiGas entered the Kashagan project as a shareholder in 2005 and later doubled its stake to 16.81 percent.

Development of the mammoth offshore field, the biggest oil discovery since Prudhoe Bay in Alaska in the 1960s, has been beset by delays, rising costs and technical complications since it was declared commercially viable 10 years ago.

Mynbayev said that Kashagan was expected to produce its first oil by the end of March 2013.

"The consortium had the intention of starting production this December, but it looks like they won't manage it. They will move it to some time around the end of March," Mynbayev told reporters on the sidelines of an international energy conference.

Kazakhstan, the world's ninth largest country by area but with a population of just 16.7 million, expects the field in the Caspian Sea to be the main driver of its plans to raise oil output by 60 percent by the end of the decade from 80 million metric tons (88.2 million tons) in 2011.

Stakes similar to that of KazMunaiGas in the North Caspian Operating Company (NCOC), the consortium developing Kashagan, are held by ENI (ENI.MI), ExxonMobil (XOM.N), Royal Dutch Shell (RDSa.L) and French energy company Total (TOTF.PA). Japan's Inpex (1605.T) has 7.56 percent.

(Additional reporting by Mariya Gordeyeva; Writing by Dmitry Solovyov; Editing by Miral Fahmy and Richard Pullin)

• A Permanent Economic Emergency