Prime Minister Vladimir Putin launched a withering attack on purported price-fixing by coal and steel producer Mechel, prompting the company's U.S.-listed stock to plunge more than 30 percent Thursday.

"I'm asking the Federal Anti-Monopoly Service to pay special attention to the problem -- and maybe even the Investigative Committee of the Prosecutor General's Office," Putin told a meeting of steel barons in Nizhny Novgorod, where he also backed calls for import duties on raw materials used in steelmaking to be canceled.

"Mechel was selling raw materials in Russia at twice the price it put on exports. And where has the margin for the state taxes gone?"

Mechel's owner, billionaire Igor Zyuzin, was reportedly ill and not present at the meeting to hear Putin's threat.

"The director has been invited, and he suddenly became ill,'' Putin said. "Of course, illness is illness, but I think he should get well as soon as possible. Otherwise, we will have to send him a doctor and clean up all the problems."

To reduce steelmakers' production costs, Putin said he backed "canceling import duties on steel raw materials, as well as on certain types of rolled products that we don't manufacture in sufficient quantities."

Domestic demand for rolled steel would reach 70 million tons by 2015, "virtually equivalent to total current production,'' Putin added.

Ilya Zhitomirsky, a spokesman for Mechel, which is the country's largest coking coal producer and sixth-biggest steelmaker, declined to respond to Putin's comments late Thursday.

Mechel fell 31.2 percent to $25.20 per depositary receipt at 2:02 p.m. in New York, from Wednesday's closing $36.61, Bloomberg reported. Other Russian steelmakers also fell. Evraz dropped 6.3 percent at the close in London, while Novolipetsk Steel fell 6.9 percent.

Mechel's first-quarter net profit rose 162 percent year on year to $500 million as global coking coal prices rose more than 200 percent to reach $300 per ton.

Putin's comments could jeopardize Mechel's plans for an initial public offering, as the company is planning to place 55 million preferred shares and has announced a price range of $50.50 to $60.50 per share.

The anti-monopoly service last week said it was bringing a price-fixing complaint against Mechel after it found evidence of monopolistic activity by Mechel affiliates. Mechel said then that it knew nothing about the purported violations.

Vladimir Zhukov, a metals analyst at Lehman Brothers, said that, in criticizing Mechel, Putin was taking aim at a broader target.

"The government is trying to [persuade] coking coal producers to enter into long-term contracts with the largest domestic customers and impose better discipline on contract pricing," Zhukov said.

Mechel said earlier this week that it had concluded fixed-price agreements on supplying coking coal to major Russian steel plants for the third quarter, and was considering longer-term contracts.

Mechel's biggest rivals in coking coal production, Evraz Group's Raspadskaya and Yuzhkuzbassugol units, have not been accused by officials of price-fixing.