The chief oil trader at TNK-BP said he would leave the Anglo-Russian oil venture, which faces an uncertain future as its owners seek to dissolve their fraught but highly lucrative partnership.

Jonathan Kollek, a veteran of trading house Marc Rich who is widely credited with building the most sophisticated in-house oil trading setup in Russia during his decade at TNK-BP, said on Thursday he would be taking a career break.

He denied a newspaper report that he would join state oil major Rosneft, which has entered talks to buy international energy company BP's one-half stake in Russia's No.3 oil company and has hired a number of executives from both TNK-BP and BP recently.

"I am leaving TNK-BP after 10 years for completely personal reasons," Kollek, vice-president for sales, trading and logistics, told Reuters.

"I am not negotiating with any other company to join them. I have not been in negotiations with any other company to join them. I am taking a break for personal reasons."

Kollek will be replaced by Yelena Lobodina, currently supply department director at TNK-BP. He will stay on through September to ensure a smooth transition and would, if needed, serve as a consultant.

Israeli-born Kollek, nephew of the late mayor of Jerusalem, Teddy Kollek, introduced long-term tenders to sell crude oil and refined products while at TNK-BP, boosting its export operations.

But Kollek's proposal to establish a trading hub in Geneva was blocked last year, triggering speculation over his future at TNK-BP, a 50-50 venture between BP and four Soviet-born tycoons led by banking-to-retail billionaire Mikhail Fridman.

Change afoot

Since BP bought a one-half stake in TNK-BP in 2003 for $7 billion, the co-owners have clashed repeatedly over strategy, leading BP in June to put up for sale its stake - now valued at around $25 billion.

The AAR consortium representing the four businessmen has entered purchase talks with BP and has expressed interest in buying half of the British-based group's stake - or 25% of TNK-BP.

Rosneft, now headed by powerful former deputy prime minister Igor Sechin, has also started talks to buy BP's entire stake, but under the TNK-BP shareholders' agreement it cannot strike any deal before mid-October.

Kollek, regarded as close to TNK-BP executive director and shareholder German Khan, denied that the shareholder dispute had played any part in his decision to step down.

"It's the best company on the planet to work for and I'm proud to have worked there, but after being in the same position for 10 years it's time for the individual and for the company to make a change," he said by telephone from London.

Industry sources did not rule out, however, that Kollek may eventually join Rosneft - following a path already taken by TNK-BP's former head of downstream operations, Didier Casimiro, and several former BP executives.

Oil traders say that Sechin has ordered a purge of the trading department and Casimiro has launched a revamp of oil and product sales by Rosneft, a company that has faced market criticism for over-investing and not focusing enough on operational efficiency.