ACCRA - Ghana has not blocked a planned $4 billion oilfield stake sale to Exxon Mobil by Kosmos Energy but still threatens to do so if the parties do not abandon the deal, a government source said on Tuesday.

The Wall Street Journal reported on Tuesday the government had blocked the deal -- something it has been threatening to do since October -- and would only allow the state oil company to buy the stake.

Kosmos agreed in the autumn to sell its 30.875 percent interest in The West Cape Three Points Block and its 18 pct stake in Deepwater Tano Block in the Gulf of Guinea to Exxon for around $4 billion, sources close to the deal said.

The government source told Reuters the government had written to Exxon about the deal but had not gone beyond repeating the threat.

We're telling them that we prefer that they don't continue ... and if they do, we'll not approve of it, the source said.

Kosmos sources have said the government can only block a contract if it can show that the potential buyer lacks sufficient technical skills or financial strength -- a hurdle that Exxon, the world's largest non-government controlled oil company, is unlikely to fail.

Analysts said if the government were to block the deal, it could face legal action from Kosmos, which is backed by U.S. private equity funds Blackstone Group LP and Warburg Pincus LLC , and that the threats to block the deal could be aimed at scuppering it without opening itself up to a lawsuit.

Exxon spokesman Patrick McGinn said the company did not comment on the details of commercial discussions or opportunities, adding only that it routinely evaluates potential development opportunities around the world.

The Jubilee field, which crosses the two blocks in which Kosmos holds stakes, has 800 million barrels of recoverable reserves, Ghanian Energy Minister Joseph Oteng-Adjei said on Tuesday.

(Additional reporting by Martinne Geller; editing by Karen Foster)

(Writing by Tom Bergin)