Yukos feels that politics played a role

However, it may take months rather than weeks to untangle the deal, analysts said, as the two sides wrangle over money and seek shareholder approval.

The tie-up was unexpectedly called off by Sibneft last month amid rumours of pressure from the Kremlin.

Yukos' largest shareholder is currently in prison facing tax and fraud charges.

Nothing signed

According to Yuri Beilin, Yukos vice president and deputy chief executive, the oil and gas giants "have reached a preliminary agreement".

But "no legal document has been signed", he added.

Any agreement "has to be approved by the board of directors, several of whom have expressed concern about certain aspects" of the break up.

Shareholders also will have to rubber stamp any agreement.

Compensation

The main sticking point may be the amount of compensation Yukos gets from Sibneft for pulling out of the merger.

Yukos indicated on Wednesday that it would not be seeking to enforce a contractual compensation payment of $1bn.

"The $1bn concerned" the "completed" merger, said Mr Beilin.

"Now we are discussing a new deal, and $1bn has not been made a condition of the new deal, because there is not a deal yet."

However, analysts said the company would want interest on the $3bn it paid as part of the deal.

Speculation

Mr Khodorkovsky's imprisonment may have prompted merger's demise

Russia's rumour mill went into full swing when Sibneft announced it was pulling out of the merger.

Speculation was rife that Roman Abramovich, the billionaire owner of London-based Chelsea football club and Sibneft's main shareholder, had met President Vladimir Putin days before the deal was called off.

Mikhail Khodorkovsky, Yukos's main shareholder and a vocal critic of President Putin, is in a Moscow prison on fraud and tax-evasion charges.

Commercial

Many analysts, however, believed that Sibneft's cold feet was related to purely commercial considerations.

According to some analysts, Sibneft was insisting on control of the combined firm, something Yukos - as by far the bigger partner, and technically the acquirer - was determined to resist.

Yukos had just installed new management, after Mr Khodorkovsky stepped aside from day-to-day control, and was unwilling to let Sibneft put its own executives at the helm.

It is also likely that Mr Abramovich had lost faith in the deal after Mr Khodorkovsky's arrest.