The S&P 500 ended a volatile session nearly flat Friday as U.S. President Donald Trump slammed China before sounding upbeat about reaching a trade deal, but the benchmark index closed out its best month of May since 1990.

The Nasdaq also registered its biggest monthly percentage gain since November 2023.

Trump's post on his Truth Social platform said China had breached an agreement with the U.S. to mutually roll back tariffs and trade restrictions for critical minerals, and issued a new veiled threat to get tougher with Beijing. He did not specify how China had violated the agreement.

Stocks pared losses as Trump said on Friday afternoon he will speak to China's President Xi Jinping and hopefully work out their differences on trade and tariffs.

Tim Ghriskey, senior portfolio strategist at Ingalls & Snyder in New York, said tariffs remain an issue for the market.

"The U.S-China trade talks supposedly have stalled again, and yet they have a meeting coming up as well," he said.

According to preliminary data, the S&P 500 lost 4.97 points, or 0.06%, to end at 5,907.20 points, while the Nasdaq Composite lost 62.11 points, or 0.32%, to 19,113.77. The Dow Jones Industrial Average rose 27.26 points, or 0.06%, to 42,242.99.

May was a volatile month for stocks as Trump's erratic trade policies kept investors on edge, but his softening tariff stance, along with upbeat earnings and tame inflation data, helped the S&P 500 rebound from its April lows.

Investors on Friday also digested data showing U.S. consumer spending increased 2.1% year-on-year in April after advancing 2.3% in March. The Federal Reserve tracks the PCE price measures for its 2% inflation target.

Traders maintained bets that the U.S. central bank would cut its target for short-term borrowing costs in September.

While the effective U.S. tariff on imports was between 2% and 3% before Trump took office, it stands at about 15%, according to Oxford Research estimates. This would have been lowered to about 6% by a trade court ruling, but an appeals court's emergency stay has kept the higher rate in place for now.

Among other big movers on the day, Ulta Beauty jumped after the cosmetics retailer raised its annual profit forecast after beating quarterly results.