Stocks in Asia tumbled Monday as investors braced for a week of market tumult caused by an expected announcement of more tariffs by President Trump on America’s biggest trading partners.

Japan’s Nikkei 225 index fell nearly 3 percent in early trading. Stocks in South Korea and Taiwan were down more than 2 percent.

Stocks in Hong Kong and mainland China were mostly unchanged, bolstered by a report signaling that China’s export-led industrial sector continues to expand despite Mr. Trump’s initial tariffs.

Futures on the S&P 500, which allow investors to trade the benchmark index before exchanges reopen in New York in the morning, slumped 0.5 percent on Sunday evening. On Friday, the S&P 500 dropped 2 percent on concerns about inflation and weak consumer sentiment.

Since taking office a little over two months ago, Mr. Trump has kept investors and companies guessing with his haphazard rollout of what he calls an “America First” trade policy.

In some cases, Mr. Trump has imposed tariffs to make imports more expensive in industries like automobiles, arguing that the trade barriers will spur investment and innovation in the United States. He has also used tariffs, and their threat, to try to extract geopolitical concessions from countries. He has further unnerved investors by saying he does not care about the fallout of his actions on markets or American consumers, who will have to pay more for many goods if import prices rise.

Over the weekend, Mr. Trump ramped up the pressure, threatening so-called secondary sanctions on Russia if it does not engage in talks to bring about a cessation of fighting in Ukraine. The tactic echoes similar sanctions concerning Venezuela. He said last week that any country buying Venezuelan oil could face another 25 percent tariff on its imports to the United States.

The threats over the weekend add to tariffs of 25 percent on imported cars and some car parts set to be implemented this week, barring any last minute reprieve. That’s in addition to previously delayed tariffs on Mexico and Canada, as well as the potential for further retaliatory tariffs on other countries.

Adding to investors’ angst is the scheduled release on Friday of the monthly report on the health of the U.S. jobs market. It could provide another reading of how the Trump administration’s policy pursuits are weighing on the economy.

Keith Bradsher contributed reporting.