MOSCOW —  Investors piled out of Russian stocks Friday after the abrupt departure from the country of a foreign oil boss and the prime minister's unexpected severe criticism of a large steel firm.

MICEX, the exchange where the bulk of trading in Russian stocks takes place, plunged by 4.8 percent as of 12:20 p.m. Russian time, while the RTS, a top stock index, lost 4.4 percent to drop beneath the critical 2000-point barrier for the first time since March.

After Prime Minister Vladimir Putin's scathing attack on Mechel late Thursday, heavy trading in New York sent the steel and coal maker's stock down by nearly 40 percent, losses mirrored Friday morning in Russian trading.

The premier criticized the company, which is the largest supplier of coal for steelmakers in Russia, for charging much higher prices for raw materials domestically than it does for its exports, and called for an antitrust investigation into its activities.

Earlier Thursday, Robert Dudley, CEO of the embattled Anglo-Russian oil producer TNK-BP, left the country three days before his visa was due to expire. Russia has not renewed the visa on the ground that he allegedly does not have a valid work contract.

The developments rattled investors, leading to a heavy sell-off in Russian stocks. The RTS is now down more than 20 percent from its mid-May high, pushing it into technical bear territory.

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