US President Donald Trump has rejected a request by oil giant ExxonMobil to bypass US sanctions against Russia, which would have enabled it to resume drilling under its Black Sea oil venture with Rosneft.
Rosneft is majority-owned by the government of Russia's President Vladimir Putin.
"The Treasury Department will not be issuing waivers to US companies, including Exxon, authorising drilling prohibited by current Russian sanctions," Treasury Secretary Steven Mnuchin said in a statement.
The decision had been made "in consultation" with Mr Trump, Mr Mnuchin added.
Earlier this week, reports emerged that ExxonMobil had applied for the waiver in 2015, after sanctions were imposed in the wake of Russia's annexation of Crimea.
According to the reports, ExxonMobil had voiced concern that it could lose its contractual exploration rights in the Black Sea if drilling operations did not recommence by the end of 2017.
Exxon and Rosneft agreed the partnership, which could see upward of $500bn invested in US and Russian oil fields, in 2012. At the time, Rex Tillerson was ExxonMobil's president and chief executive.
Mr Tillerson now serves as US Secretary of State.