NEW YORK (AP) — Stocks tumbled again Friday, and this time bond yields joined in the swoon as worries about an imminent Russian invasion of Ukraine piled onto Wall Street's already heavy list of concerns about inflation and interest rates.

The S&P 500 lost 1.9% after the White House encouraged all U.S. citizens to leave Ukraine within the next 48 hours, before  possible military action by Russia. The price of oil rose more than 3%.

Stocks took a sudden turn lower in the middle of trading, with losses for the S&P 500 nearly tripling in about half an hour. Similar, knee-jerk swings swept through other markets as investors pulled money out of riskier things like stocks and moved instead toward the safety of bonds and gold.

They're just the latest sharp veers in what's already been a tumultuous 2022 for markets. Wall Street has been shaking as it comes to grips with a Federal Reserve forced to aggressively remove the low interest rates that investors love, in order to beat back high inflation.

The S&P 500 fell 85.44 points to 4,418.64 to lock in its first weekly loss in the last three but its fourth in the last six. The Dow Jones Industrial Average lost 503.53, or 1.4%, to 34,738.06, and the Nasdaq dropped 394.49, or 2.8%, to 13,791.15.

Tensions have been simmering for a while about possible military action by Russia, and U.S. national security adviser Jake Sullivan said Friday that the United States did not have definitive information that Russian President Vladimir Putin had ordered an invasion. But he also said that "the threat is now immediate enough that prudence demands that it is the time to leave now" for Americans in the country.

Russia is one of the world's largest energy producers, and the warnings gave oil prices an immediate jolt. Brent crude, the international standard, rose 3.3% to settle at $94.44 barrel amid the possibility that violence could disrupt supplies. U.S. crude rose 3.6% to settle at $93.10 per barrel.

Prices were already rising before the Ukraine warnings, likely because of a statement from the International Energy Agency that supplies in the oil market are already tight, said Stewart Glickman, energy equity analyst at CFRA.

Gold also rose, gaining nearly $20 in half an hour during the afternoon to top $1,860 per ounce, as investors searched for safety.

A similar rush for stability also drove investors in Treasury bonds, which in turn lowered their yields. The 10-year Treasury yield sank to 1.91% from roughly 2.03% late Thursday.

For bond yields, it's a sharp U-turn after they steadily marched higher on expectations that the Fed will raise rates more often and by a sharper degree this year than expected. Just a day earlier, the 10-year yield topped 2% for the first time since 2019.

Forecasts for a more aggressive Fed got a huge jolt on Thursday, when a report on inflation came in hotter than expected and showed that it was at a 40-year high. The Fed can slow the economy and inflation by raising interest rates, something it hasn't done since 2018, but higher rates also put downward pressure on stocks and other investments.

Economists at Goldman Sachs just increased their forecast for rate increases this year by the Fed to seven from five, for example.

Much of the market's volatility in early 2022 has centered around expectations for what the Fed will do. Besides Thursday's report on inflation, other flashpoints included the release of the minutes of a Fed policy meeting that said it may reverse its bond-buying program earlier than expected.

The market also shuddered earlier this month after Facebook's parent company reported surprisingly weak results for its latest quarter. That threatened the belief that continued profit growth can help stocks power through the downward pressures created by higher rates.

Markets will likely remain volatile as the Fed moves closer to raising rates.

"What we're going through is likely going to continue in the short run," said Chris Zaccarelli, chief investment officer for Independent Advisor Alliance.

The prospect for violence in Ukraine only adds more uncertainty, though some on Wall Street said it will ultimately likely recede in importance to markets.

"You can't minimize what today's news could mean on that part of the world and the people impacted, but from an investment point of view we need to remember that major geopolitical events historically haven't moved stocks much," Ryan Detrick, chief market strategist for LPL Financial wrote in a research note.

"For instance, after JFK was assassinated in November 1963 stocks went on one of their best 6 month runs ever. The truth is a solid economy can make up for a lot of sins."

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AP Business Writer Cathy Bussewitz contributed.