But they appeared to win no quick concessions.
Under WTO rules, such countermeasures have to be in place within 90 days of the USA tariffs entering force.
The American president made his comments after crunch talks in Brussels between European Union negotiators and US Trade Representative Robert Lighthizer in an effort to defuse a bitter row that many fear could turn into an all-out trade war. Canada and Mexico, both members of the North American Free Trade Agreement, also warned that they would take strong countermeasures.
"Day of meetings in Brussels with Minister @SekoHiroshige & @USTradeRep Lighthizer". PM tweeted "Great discussion today on security and trade". Not fair or sustainable. "We have large trade deficits with Mexico and Canada".
"We don't carry out a global FONOPs program as the United States does", she said.
"He is committed to having a very fair and reciprocal military and trade relationship", Trump said on Twitter, referring to Turnbull. "If they drop their horrific barriers and tariffs on USA products going in, we will likewise drop ours".
Such import taxes on cars would be especially problematic for Germany, a German foreign trade expert said on Sunday.
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Key U.S. trading partners and businesses have warned the tariffs could backfire, provoking a trade war and hurting allies like the European Union and Japan more than China, their main target. They're not all-encompassing. He's not going to impose tariffs on every product that comes into the United States, but he is going to act in defense of US industries that have been especially hurt by unfair trade practices, as he should. He was apparently referring to the European Union threats of retaliation.
Trump on Friday said Australia would become the third country to be free from a 25 percent tariff on steel imports and 10 percent for aluminum.
But the United States would like Australia to carry out such patrols, which would mean sailing within 12 nautical miles of territory Beijing has unilaterally claimed, including islands it has built, to demonstrate Australia does not recognise Beijing's claims under global law.
The U.S. reported a $375 billion deficit with China past year, so a 20 percent reduction would still be among the largest trade gaps that it has with any country.
"There's still some time [before the tariffs kick in]", Seko said, indicating that the government planned to continue urging the United States to exempt Japanese steel and aluminum.
While there are several factors behind the rising deficit with its non-FTA partners, the simple fact is that the FTAs the USA have clinched - comprising 40 percent of its total trade - have opened markets to the benefit of US exporters.
The tariffs were aimed at China, which has been dumping cheap, subsidized steel into the USA and undercutting American producers who have been forced to slash production and jobs.
The EU has warned that it stands ready to slap "rebalancing" tariffs on about 2.8 billion euros ($3.4 billion) worth of US steel, agricultural and other products, like peanut butter, cranberries and orange juice.