Benchmarks in London, Frankfurt, Shanghai and Tokyo all declined, as did Wall Street futures.
Trump alarmed investors by saying he had $325 billion of Chinese imports available for additional tariffs "if we want." That shook markets that had been reassured by Trump's June agreement with Chinese President Xi Jinping to resume trade negotiations.
The Chinese government warned tariff hikes would "create a new obstacle" in talks on ending their bruising fight over Beijing's technology ambitions.
Trump's comment "cast a dark cloud over lingering concerns on trade talk progress," Mizuho bank analysts said in a report.
In Europe, London's FTSE 100 fell 0.3% to 7515 and Frankfurt's DAX declined 0.4% to 12,288. France's CAC-40 edged up 0.2% to 5,582.
On Wall Street, futures for the Standard & Poor's 500 index and the Dow Jones Industrial Average were down 0.1%.
Corporate earnings reports are getting into full swing this week, and investors have been mostly cautious in their assessments of them. Earnings are still expected to decline for S&P 500 companies in the second quarter.
Shares in Netflix were down 11% in premarket trading after the company said its subscribers in the U.S. dropped.
In Asia, the Shanghai Composite Index lost 1% to 2,901.18 and Tokyo's Nikkei 225 tumbled 1.9% to 21,046.24. Hong Kong's Hang Seng retreated 0.5% to 28,438.99 and Seoul's Kospi was 0.3% lower at 2,066.55. India's Sensex lost 0.4% to 39050.29.
Sydney's S&P-ASX 200 shed 0.4% to 6,649.10. Taiwan and New Zealand gained while Southeast Asian markets were mixed.
Japan reported June exports declined 6.8% from a year earlier. Imports fell 5.2%. For the first six months of this year, Japanese exports slipped 4.7% while imports edged 1.1% lower.
"Continued weak global production and cautious approaches to fixed investment will likely weigh on Japan's exports over the near term," Harumi Taguchi of IHS Markit said in a report.
The South Korean central bank cut its benchmark rate for a one-year loan by 0.25 percentage points to 1.5%. It was the first reduction since 2016. The Bank of Korea cut its 2019 economic growth forecast by 0.3 percentage points to 2.2%.
ENERGY: Benchmark U.S. crude rose 45 cents to $57.23 per barrel in electronic trading on the New York Mercantile Exchange. The contract fell 84 cents on Wednesday to close at $56.78. Brent crude, used to price international oils, rose 60 cents to $64.26 in London. It lost 69 cents the previous session to $63.66.
CURRENCY: The dollar declined to 107.90 yen from Wednesday's 107.98 yen. The euro edged down to $1.1218 from $1.1226.