World stock markets plunged and oil prices surged by nearly $6 per barrel Thursday after President Vladimir Putin launched Russian military action in Ukraine.

Market benchmarks tumbled in Europe and Asia and U.S. futures were sharply lower. Brent crude oil jumped to over $100 per barrel on unease about possible disruption of Russian supplies. The price of U.S. benchmark crude briefly surpassed $98 per barrel.

The ruble sank 7.5% to more than $87 to the U.S. dollar.

The future for Germany's benchmark DAX index lost 5.3% and London's FTSE 100 was off 3.3% as Europe awakened to news of explosions in Kyiv, Kharkiv and other areas of Ukraine.

Putin said Russia's military operation was needed to protect civilians in eastern Ukraine, a claim Washington had predicted he would make to justify an invasion.

President Joe Biden denounced the attack as “unprovoked and unjustified" and said Moscow would be held accountable, which many took to mean Washington and its allies would impose additional sanctions. Putin accused them of ignoring Russia’s demand to prevent Ukraine from joining NATO and to offer Moscow security guarantees.

“The relief rally has quickly reversed course,” said Jeffrey Halley of Oanda in a report. “Equities are tanking in Asia.”

Both U.S. and Brent crude oil were hovering near $100 per barrel by early Thursday European time.

Benchmark U.S. crude was $5.66 higher at $96.76 per barrel in electronic trading on the New York Mercantile Exchange. The contract fell 25 cents to $92.10 on Wednesday.

Brent crude, the price basis for international oils, advanced $5.41 to $99.46 per barrel in London. It lost 20 cents to $94.05 the previous session.

On Wednesday, Wall Street's benchmark S&P 500 index fell 1.8% to an eight-month low after the Kremlin said rebels in eastern Ukraine asked for military assistance. Moscow had sent soldiers to some rebel-held areas after recognizing them as independent.

Washington, Britain, Japan and the 27-nation European Union earlier imposed sanctions on Russian banks, officials and business leaders. Potential options for more penalties including barring Russia from the global system for bank transactions.

In Asia, the Nikkei 225 in Tokyo fell 1.8% to 25,970.82 and the Hang Seng in Hong Kong lost 3.5% to 22,823.26. The Shanghai Composite Index shed 1.7% to 3,429.96.

Asian economies face lower risks than Europe does, but those that need imported oil might be hit by higher prices if supplies from Russia, the third-largest producer, are disrupted, forecasters say.

The Kospi in Seoul lost 2.6% to 2,648.80 and Sydney's S&P-ASX 200 fell 3% to 6,990.60.

India's Sensex was down 3.1%, New Zealand lost 3.3% and Southeast Asian markets also fell.

Investors already were uneasy about the possible impact of the Federal Reserve's plans to try to cool inflation by withdrawing ultra-low interest rates and other stimulus that boosted share prices.