Katainen said Brussels was seeking "clarity" on how the tariffs will be implemented as the 28-nation bloc argued it should be excluded because its industry was not a security threat to Washington.
Trump imposed the tariffs - 25 percent on steel and 10 percent on aluminium - despite repeated warnings from the European Union and other allies that this could trigger a full-scale trade war.
After Trump opened the door, Brazil, Japan, South Korea, Australia and Europe clamored for special treatment, while Chinese producers called on Beijing to retaliate in kind.
"President Trump has recently said, and I quote, 'trade wars are good and easy to win, '" Tusk told a press conference in Luxembourg. "We also hope to convince the USA administration that this is not the right move".
EU To Respond To US Tariffs Within 90 Days If Not Exempt
Treasury Secretary Steven Mnuchin earlier said he expects countries in addition to Mexico and Canada to be exempted in the next couple of weeks.
Those threats have been overblown, according to Dani Rodrik, professor of global political economy at Harvard University's John F. Kennedy School of Government and one of the world's leading experts on trade.
Announcing the tariffs, Trump said Canada and Mexico would be excluded and other countries could negotiate exemptions, but he singled out Germany for particular criticism.
Malmstroem said the EU was still trying to persuade Washington not to go ahead with the tariffs, which she said would threaten "thousands of European jobs".More news: 'Pharma Bro', who drove up anti-HIV drug prices, gets jail
She said, "trade creates wealth, when it is based on exchange and cooperation" and added, referring indirectly to the surprise resignation of Trump's top economic adviser Gary Cohn Tuesday, that, "advocates for this in the USA administration are very important".
Brazil, which after Canada is the biggest steel supplier to the USA market, said it wanted to join the exemption list, and Argentina made a similar case.
Japan, the United States' top economic and military ally in Asia, was next in line. Th U.S. justified these tariffs by citing national security!
Speaking at a panel discussion in Brussels, the European Union's trade commissioner Cecilia Malmstrom criticized Trump's decision to impose tariffs on steel and aluminium products.More news: How Republicans tried to change Trump's mind on tariffs
European Union trade commissioner Cecilia Malmstroem said a full-on transatlantic trade war was "not in anybody's interests" - a stark contrast from Mr Trump, who last week declared trade wars were "good and easy to win".
Malmstrom said she would discuss the issue at a long-planned meeting on Saturday with US Trade Representative Robert Lighthizer and his Japanese counterpart Hiroshige Seko, noting that it was "not crystal clear" what Trump had decided Thursday.More news: Tough day for Aussies in South African test
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