UPDATE 2-Rival candidates vie to run Russian oil firm TNK-BP

* Two nominees for the post of CEO

* BP nominee Pavel Skitovich joined by Maxim Barsky

* Russia-backed shareholders plan to appoint interim CEO

* Interim CEO could run company for 3-6 months (Adds quotes, details, background)

By Katya Golubkova and Robin Paxton

MOSCOW, May 26 (Reuters) - Oil major BP (BP.L) is squaring up for another battle over the management of its TNK-BP venture, after its Russian partners on Tuesday proposed an alternative to BP's candidate for running Russia's No. 3 oil producer.

The quartet of Russia-connected billionaires who own half of TNK-BP also plan to appoint an interim chief executive from within their own ranks to run the company for up to six months, sources close to both shareholder groups told Reuters. "I think a new person from AAR will be appointed for three to six months as a temporary chief executive and that this will be fair. Last time, it was a BP person," said a source close to AAR, or Alfa-Access-Renova, which represents the Russian group.

A quarrel between BP and the Russia-connected shareholders last year led to the departure of many expatriate TNK-BP staff, including then Chief Executive Robert Dudley, and raised concerns among foreign investors about doing business in Russia.

Though both sides say they have resolved their differences, the appearance of a second candidate to replace current CEO Tim Summers -- whose contract expires on June 1 -- suggests tough negotiations lie ahead.