U.S. oil giant ExxonMobil began drilling in Russia's Arctic on Saturday, despite Western sanctions imposed on its Russian partner Rosneft, and was hailed by Russia's president as an model of "cooperation."

Although U.S. sanctions over the crisis in Ukraine are not designed to halt joint projects by Russian and U.S. companies, they nevertheless aim to starve Rosneft of dollar financing and ban access to modern technology.

"Today, commercial success is driven by efficient international cooperation," Vladimir Putin told Rosneft CEO Igor Sechin and Glenn Waller, ExxonMobil's lead manager in Russia, on a videoconference call from his Black Sea residence in Sochi.