WASHINGTON, United States — Several US senators have called for an investigation into whether President Donald Trump engaged in insider trading or market manipulation by encouraging people to buy stocks just before his dramatic reversal on global tariffs.

"Who in the administration knew about Trump's latest tariff flip flop ahead of time? Did anyone buy or sell stocks, and profit at the public's expense?" California Democratic Senator Adam Schiff posted on X on Wednesday.

"I'm writing to the White House -- the public has a right to know," he added.

Democratic members of the House Financial Services Committee wrote on X that "the President of the United States is literally engaging in the world's biggest market manipulation scheme."

The accusations came as Trump posted a few minutes after Wall Street opened that "IT'S TIME TO BUY".

A few hours later, he announced a 90-day suspension of additional tariffs against dozens of countries, with the exception of China, triggering a historic stock market rebound.

After several days of collapse, the Dow Jones index ended Wednesday up 7.87 percent, its biggest gain since 2008, and the Nasdaq up 12.16 percent, the most since 2001.

Trump also signed his post on Truth Social with the letters "DJT" -- both his initials and the stock market abbreviation for his media company, Trump Media & Technology Group. The company's shares closed the day up 21.67 percent.

White House communications adviser Margo Martin posted a video on X late Wednesday showing Trump receiving Charles Schwab, founder and co-chairman of the Schwab asset management, in the Oval Office.

"This is Charles Schwab," Trump said, introducing the 87-year-old billionaire to champion car racers.

"He's not just a company, he's actually an individual! And he made 2.5 billion (dollars) today," he said.

Former White House ethics lawyer Richard Painter also felt there was a case for investigation.

"Presidents are not investment advisors," said Painter, who had served under the administration of former president George W. Bush.

"This scenario could expose the president to charges of market manipulation," he told NBC.

The White House said Trump only wanted to "reassure" the public.

"It is the responsibility of the president of the United States to reassure markets and Americans about their economic security in the face of constant media scaremongering," White House spokesperson Kush Desai told the Washington Post.