NEW YORK—U.S. stocks opened lower Friday in what was expected to be another volatile session, as fears of a Greek default and the domestic economy spiraling into another recession continued to feed investor trepidation.

The Dow Jones Industrial Average was off 21 points, or 0.2%, to 10716. The index plunged 675 points in the last two sessions and is down more than 7% this week, on pace for its worst weekly performance since the financial crisis.

The Dow is also down more than 16% from its April high, inching closer to the 20% drop that would signal a new bear market.

The Standard & Poor’s 500-stock index fell one point to 1129 and the technology-heavy Nasdaq Composite also fell one point to 2454.

Increasing fears of a global economic slowdown and the markets’ strong downside momentum overshadowed the assertion by officials of the G20 economies that they were committed to keeping the financial system stable and to shoring up growth.

There’s a growing sense among investors that governments and central banks will be unable to get growth back on track. The Federal Reserve’s gloomy economic outlook has alarmed investors and resulted in a steep selloff ranging from stock to corporate bonds, as well as oil and gold.

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