Russian President Vladimir Putin on Friday said he expected metals giant Norilsk Nickel to fully restore the environment after an unprecedented Arctic fuel spill, as responders said they had managed to stop the slick from spreading further.

A national-level state of emergency was announced after 21,000 tonnes of diesel fuel spilled from a reservoir that collapsed last Friday outside Norilsk, polluting huge stretches of river in remote tundra with bright red patches visible from space.