Foreign investors in Russia have been served a costly reminder of the political risks of doing business there after a few sentences from Vladimir Putin, the prime minister, wiped out half the value of a New York-listed steelmaker.

Mechel's shares plummeted after Mr Putin accused Igor Zyuzin, its majority owner, of price-gouging and tax evasion. Before the remarks Mr Zyuzin ranked as Russia's 12th richest man with a fortune estimated at $11bn. Yesterday his worth was about $5.5bn (€3.5bn, £2.7bn).