rosneft exxon
Rosneft Chief Executive Igor Sechin and Exxon Mobil Chief Executive Rex Tillerson take part in a signing ceremony at a Rosneft refinery in the Black Sea town of Tuapse in southern Russia, June 15, 2012. Reuters

Exxon Mobil (NYSE: XOM) CEO Rex Tillerson will speak on Monday at a summit in Moscow, according to the program’s online schedule, despite requests from the U.S. government to isolate Russia over its actions in Ukraine.

Gazprom, Russia’s state-controlled gas company, stopped supplying natural gas on credit to Ukraine on Monday, saying it will only supply gas that Ukraine pays for, the New York Times reported. Ukraine claims Gazprom is overcharging.

Tillerson’s scheduled speech at the World Petroleum Congress, a major industry event hosted by an independent organization every three years, takes place just a few months before Exxon plans to drill its first well in Russian Arctic waters with Rosneft, Russia's state-controlled oil company. The U.S. said it won’t send government officials to the meeting and discouraged U.S. senior executives from attending.

Exxon’s chief will stand with Rosneft’s chief, Igor Sechin, who is closely tied to Russian President Vladimir Putin, even though the U.S. placed sanctions on him in April. The sanctions prevent Sechin from traveling to the U.S. and ban American citizens from conducting business with him, but not his company.

The two companies signed an agreement in May in St. Petersburg at a business forum that solidified the joint project to drill in the Arctic and Siberia and to liquefy natural gas for export to the Far East, while the U.S. and Europe discussed whether to impose harsher sanctions on Russia to condemn its treatment of Ukraine. Many U.S. companies boycotted the forum after the U.S. State Department suggested that they do so.

The partnership with Russia’s massive oil producer is one of Texas-based Exxon’s most promising opportunities to find new oil reserves. Initial drilling in August is expected to cost $3.2 billion and could hold billions of barrels of oil, though it would be years before the companies could produce meaningful amounts of crude from the Arctic well.

Aside from the gas war, Ukrainian officials have accused Russia of rolling tanks into their country to support pro-Russian separatists. The U.S. and other countries have backed Ukraine’s claim, but Russia has denied arming the separatists.