* Telenor boosted Vimpelcom stake in Feb deal with Weather
* Alfa claims Telenor, Weather formed a "group" owning over 50 pct
* Says Telenor, Weather should have launched mandatory tender offer (Adds details, background, Telenor comment, analyst quote)
By Maria Kiselyova
MOSCOW, June 5 (Reuters) - Russian billionaire Mikhail Fridman's Alfa Group on Tuesday cried foul over Telenor's stake increase in Vimpelcom, reigniting hostilities between the shareholders and indicating it wants a bigger role in the telecoms group.
Fridman, also at loggerheads with its partner BP in Russia's third-biggest oil firm TNK-BP, may be seeking to restore his power at Vimpelcom after being weakened by the recent Telenor deal, analysts said.
Vimpelcom said on Tuesday that Altimo sent it a letter, claiming that Telenor and Egyptian tycoon Naguib Sawiris's Weather Investments violated the company's bye-laws.
"We think Altimo wants to restore their power in the supervisory board in the company ... and then there might be different scenarios - either increasing the stake at an attractive price or selling its stake," said Viktor Klimovich, analyst at VTB Capital.
Altimo claimed Telenor and Weather formed a "group" owning more than a 50 percent voting interest in Vimpelcom via their deal in February and requested Vimpelcom to preserve the status quo at the supervisory board level.
Telenor denied it was in any partnership with Weather.
"Telenor is not in partnership or in a group with Sawiris, so this is absurd," said Telenor spokesman Dag Melgaard.
"We see this as an attempt to push Vimpelcom's share price down, since we are approaching a point in the calendar, 11th June, where they can buy shares in the company," he added.
Telenor boosted its voting stake in Vimpelcom to 36.36 percent in mid-February after a deal with Weather, taking back partial control of the company from Alfa's telecoms arm Altimo - with which it has fought a years-long corporate battle.
Analysts have said the deal threatened to renew the shareholder fight for influence over Vimpelcom - conflict that has come to typify the difficulties faced by overseas investors in Russia's oligarch-dominated business world..
The deal has been opposed by Russia's state competition watchdog, which filed a lawsuit in a Moscow court seeking to undo the transaction, alleging it violated the Russian Strategic Investment Law.
Altimo may start to increase its Vimpelcom stake this month when a 12-month standstill agreement, signed about a year ago, expires.
Altimo, the telecoms arm of Alfa Group, declined to comment beyond the statement. (Additional reporting by Joachim Dagenborg in Oslo and Megan Davies in Moscow; Editing by John Bowker and David Cowell)