National Economic Council Director Kevin Hassett, a top economic advisor to Trump, on Monday rebuked concerns about tariff-related inflation. The Fed, Hassett told CNBC, has been "very, very wrong" in its assessment of a potential resurgence of price increases.

President Donald Trump recently issued a raft of new tariff threats, including steep rates on dozens of countries and a new duty on copper imports.

President Trump has taken an unconventional approach to trade negotiations by sending form letters to foreign leaders.

Italy's foreign minister warned that, while he hopes for successful negotiations, the EU will respond resolutely to Trump's latest tariff threat.

European shares ended slightly lower on Monday, with tariff-sensitive auto stocks down after U.S. President Donald Trump's latest threat to impose steep tariffs on the European Union, though gains in financials and healthcare kept losses in check.