The Russian authorities' withdrawal of a key permit for a Shell-led natural gas project follows months of pressure on three large foreign energy investments in the country that has come to a head in recent days.

The three - Exxon-Mobil's Sakhalin-1 project and Shell's Sakhalin-2, both on an island in the Russian far east, and a Total-led venture in the Arctic Circle - are all so-called production-sharing agreements (PSAs).