European gas prices spiked by 24% today, hitting their highest level this month and almost seven times that of a year ago, after Russian energy giant Gazprom cut off all gas exports to Poland and Bulgaria.

Kremlin-owned Gazprom, the world’s biggest natural gas company, has warned that the taps to these “unfriendly” countries will remain off until they agree to pay for gas in Russian roubles.

The move, which is an attempt to boost the rouble, is Moscow’s toughest response yet to the crippling sanctions imposed by the West for its invasion of Ukraine.