Russian security forces have raided the Moscow offices of BP in a search for documents related to the British oil giant’s failed attempt to sign a deal with Russia to extract oil from the Arctic.

About 15 black-clad special force officers sealed off the firm’s headquarters Wednesday, sent most workers home and began their search. BP said it did not think there was “any legitimate basis” for the raid and that work in the office was “illegally being interfered with.”

The raid came a day after Russia’s top oil producer, Rosneft, signed a $3.2 billion deal with the world’s largest energy company, U.S.-based Exxon Mobil, to explore for oil in the Kara Sea in the Arctic, as well as in the Black Sea. The deal gives Exxon — not BP — access to what are believed to be some of the world’s largest untapped reservoirs of oil and natural gas.

The Exxon-Rosneft agreement replaced a similar deal BP had once envisioned with the Russian oil producer. Like the Exxon agreement, BP’s deal with Rosneft was personally sanctioned by Prime Minister Vladimir Putin.

But BP’s pact collapsed earlier this year when minority shareholders in the firm’s Russian venture, TNK-BP, claimed in a lawsuit that the planned Rosneft venture infringed on their own business rights with BP. A court in Siberia plans to start a hearing in the case in October, and earlier this week ordered BP to produce documents related to its aborted deal with Rosneft.