BP said Tuesday that it had received visas for 24 of 148 employees who were suspended from assignments to TNK-BP one month ago amid mounting pressure against the Russian-British oil firm.

Yet the employees, who got their visas Monday, have so far been barred from entering and working at TNK-BP's offices in central Moscow, two sources inside the company said.

The 148 employees were suspended from working at TNK-BP on March 25. Recent pressure against the company has seen an employee charged with industrial espionage, a raid on TNK-BP and BP offices in Moscow, and the announcement of a state agency's environmental investigation into the company's largest oil field.

"For now, we have 24 specialists with all the proper documentation to resume work," BP spokesman Vladimir Buyanov said. He said the company expected the remaining 124 employees to receive their visas and work permits, calling it an "ongoing process" that would happen "group by group."

The employees are technically employed by BP, but were assigned to TNK-BP, the country's fourth-largest oil firm, which is half-owned by BP and half by three Russian billionaires.

The Russian shareholders -- Mikhail Fridman of Alfa Group, Viktor Vekselberg of Renova and Len Blavatnik of Access Industries -- last week issued a strong statement denying any intention to sell out, following widespread speculation that they would soon cede their stakes to state-owned Gazprom.

Buyanov declined to comment on the employees' ban on reinstatement at TNK-BP, but acknowledged, "They are not yet in the TNK-BP office."

"They have all the documents needed to resume work in TNK-BP," he added. The employees received visas and work permits tying them to BP, which maintains several projects in Russia in addition to TNK-BP, including exploration of oil fields at Sakhalin with state oil giant Rosneft.

Russia accounts for 25 percent of BP's total production.

TNK-BP spokeswoman Marina Dracheva declined to comment on the employees' ban. "It's all very much in BP's hands," she said, referring to the visa issue.

A spokesman for the Federal Migration Service, which issues visas, reiterated claims that the muddle resulted from an internal struggle within the company.

"We never had any complaints against them," Konstantin Poltoranin said.

Sources have said the visa issue arose amid a struggle that pitted Fridman and his partner in Alfa Group, TNK-BP executive director German Khan, against Vekselberg, who is more reluctant to sell.

Vekselberg said in January that he would consider selling his stake in TNK-BP if his $60 billion valuation -- a figure nearly double the company's current market capitalization -- were met.