Billionaire investor Carl Icahn issued a warning about U.S. tariffs on Monday, noting protectionist trade policies have brought about stock-market crashes.

"With tariffs, it's a very dangerous game you're playing," said Icahn, who supports President Donald Trump. "It helped bring the crash in 1929. I'm not a great supporter of that."

The Trump administration has slapped tariffs on billions of dollars worth of imports, including those coming from China, the United States' biggest trade partner. Several partners have retaliated with levies of their own on U.S. goods, including China. The administration's aim has been to level the playing field on trade between the U.S. and other countries.

"As far as I'm concerned, I think it's extremely dangerous," Icahn said on CNBC's "Halftime Report." "This is a question that ... has so many variables that you don't know which way it could go."

Icahn added he thinks Trump will ultimately do "what I consider to be the close-to-right thing."

"Hopefully, that will be settled," he said.

His comments come after the Dow Jones Industrial Average and S&P 500 dropped more than 4 percent last week. Equities fell along with global markets as investors fretted about rising borrowing costs potentially slowing down the world economy, in addition to the trade war.