Russian oil company Yukos completed a merger with a smaller rival Friday, even as government officials stepped up a criminal investigation of the giant producer.

Russian oil company Yukos completed a merger with a smaller rival Friday, even as government officials stepped up a criminal investigation of the giant producer. Russia's General Prosecutor's Office sent investigators to comb through Yukos offices, a business club and a Yukos-funded orphanage as part of the probe, widely considered a politically motivated campaign. Irina Alyoshina, deputy head of the special cases department in the prosecutor's office, told the ITAR-Tass news agency that the probe focused on alleged tax evasion running into millions of U.S. dollars. The Yukos-Sibneft merger created the world's fourth-largest company in terms of oil production. The new company will be named YukosSibneft and will generate $15 billion in annual revenues and have an estimated market value of about $35 billion, officials said Friday. With daily oil output expected at 2.06 million barrels, YukosSibneft will become the world's fourth-largest oil producer, behind ExxonMobil, BP and Royal Dutch Shell. It will have total reserves of around 19.4 billion barrels of oil equivalent. Meanwhile, Russian prosecutors kept up the pressure on Yukos, sending teams into a business club in Zhukovka and an orphanage in Zvenigorod, both on the outskirts of Moscow. Investigators removed a computer hard disk and documents were removed from the orphanage, which looks after about 100 children from regions where Yukos operates, the Interfax news agency said. It was unclear whether anything was removed from the business club. The General Prosecutor's Office told Interfax that both searches were linked to the ongoing probe into activities by Platon Lebedev, one of Yukos' top shareholders.