The Nikkei share average <.N225> fell as much as 1.46% to 23,186.84. It pared some losses to 23,278.67 by 0152GMT, down 1.07%.
The index also managed to climb above its 25-day moving average of 23,245, a key technical level.
President Trump on Monday said he would impose tariffs on steel and aluminium imports from Brazil and Argentina, raising worries he could also re-escalate trade tensions with China.
Data from the U.S. Institute for Supply Management (ISM) showed the U.S. manufacturing sector contracted for a fourth straight month in November, hurting the market's optimism that was sparked by strong manufacturing survey reading from China on Monday.
China on Monday banned U.S. military ships and aircraft from visiting Hong Kong and slapped sanctions on several U.S. non-government organisations in a response to U.S. legislation passed last week supporting protests in the Asian financial hub.
"Should Trump impose the so-called fourth tariffs on China on Dec. 15, it would be a completely different scenario from what most investors are expecting," said Masayuki Kubota, chief strategist at Rakuten Securities.
Investors have hoped that Washington will avoid imposing an additional 15% tariff on about $156 billion worth of Chinese products on Dec. 15 as part of "phase one" trade deal.
The broader Topix shed 0.9% to 1,699.04. A wide range of shares dropped on the main board, with decliners outnumbering gainers by a ratio of 83 to 17.
Among large caps, Softbank Group fell 2.3%, while Hitachi dropped 1.4%.
Pigeon tumbled 15.7% after the baby goods maker slashed its annual outlook following weak quarterly results.
Nomura Holdings bucked the trend to rise 1.7% to a 1 1/2-year high after the country's top securities brokerage firm and investment bank picked joint operations chief Kentaro Okuda to lead its turnaround.
The reshuffle was announced on Monday as Nomura posted its strongest quarterly profit in more than 17 years.
Shares of Nintendo also hit a 1 1/2-year high.
(Reporting by Tokyo Markets Team; editing by Uttaresh.V)