The targets include steel, agricultural and other products, including bourbon, peanut butter, cranberries and orange juice..
More than $3 billion worth of US goods - from bourbon and corn to Harley Davidson motorcycles - are now under a 25 percent tariff in the European Union, in retaliation for the Trump administration's tariffs that hit the EU, Mexico and Canada earlier this month.
"The rules of worldwide trade, which we have developed over the years hand in hand with our American partners, can not be violated without a reaction from our side", Malmstrom added, calling the European Union response "measured, proportionate and fully in line with WTO rules".
The European Union has announced a new range of retaliatory tariffs against the United States, in response to the USA revoking the EU's exemption from steel and aluminum tariffs. Europeans claim that breaks global trade rules.
Analyst Bergqvist argued that his "main concern" over a trade war was the impact on stock markets - and the subsequent knock-on effect for the world economy.
The spat comes amid a wider push by President Trump's administration to hit other countries with tariffs that would reduce the USA trade deficit.
"The fast-shrinking Chinese investment in the U.S. reflects the damage being done to China-U.S. -trade relations.by the trade crusade of Trump and his trade hawks", it said.
The US and European Union have imposed mutual tariffs.
Gao's comments come two days after President Trump directed his top trade official to identify $200 billion more worth of Chinese goods that will be subject to tariffs, escalating the ongoing trade dispute.
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"The rules of worldwide trade, which we have developed over the years hand in hand with our American partners, can not be violated without a reaction from our side", she said.
But US Assistant Secretary of State for European and Eurasian affairs Wess Mitchell said on Thursday that Trump's approach towards his allies was about "strategic renovation".
The world's most-powerful central bankers this week warned that escalating worldwide trade tensions have started damaging confidence among companies, threatening the global economic expansion.
The EU has also filed a case contesting the legality of the US tariffs with the World Trade Organization.
Trump ran for the presidency on a vow to topple seven decades of American policy that had favored ever-freer trade among nations.
The equivalent value of €2.8 billion worth of United States goods that will be hit by import duties charged by the EU.
It had previously registered the move with the World Trade Organization (WTO).
"While average trade-weighted US -imposed tariffs on its imports are lower than those imposed by the EU, Canada, Mexico and China, the difference is marginal", he noted.