UPDATE 2-BP Russian venture struggles with visas, tax probe

(Adds tax evasion investigation, company confirmation)

By Dmitry Zhdannikov

MOSCOW, March 25 (Reuters) - Russia raised pressure on BP's (BP.L: Quote, Profile, Research) joint venture on Tuesday as the Interior Ministry said it was probing a big tax evasion case while TNK-BP itself said it is struggling to renew visas for almost 150 employees from BP.

The news follows last week's raids of TNK-BP, half owned by BP and half by a group of Russian billionaires, and the arrest of an employee for suspected industrial espionage.

Analysts have given conflicting views about the reasons of the crackdown, with theories ranging from the Kremlin putting pressure on the Russian owners to sell out, to infighting between different Kremlin clans, or a renewed dispute between the Russian and British shareholders within the firm itself.

The pressure comes as ties between London and Moscow hit their lowest point since the Cold War, although President-elect Dmitry Medvedev again denied any political motivation behind the events around Russia's No. 3 oil firm.

The Interior Ministry said on Tuesday it was investigating tax evasion worth over $40 million involving Sidanco, an oil unit which TNK-BP liquidated in 2005 after merging it with other assets during a consolidation.

"The investigative department of the ministry has opened a criminal investigation against Sidanco according to the article 199 of the Criminal Code, part 2 -- large-scale tax evasion," said Angela Kastuyeva, spokeswoman for the department.

She said the sum involved was over 1 billion roubles ($42.2 million).