Warren Buffett criticized tariffs and trade wars during Berkshire Hathaway's annual shareholder meeting in Omaha, Nebraska, on May 4.

Investors kickoff the week awaiting more developments on President Trump’s trade deals and the decision on interest rates by the Federal Reserve out Wednesday. Optimism is improving after the S&P 500 notched the longest winning streak in 20 years last week.

Buffett, whose Berkshire Hathaway will host its annual meeting this Saturday, has held his tongue on what Trump’s tariffs mean for economies and markets.