The EU and Japan held crunch talks with their United States counterparts in Brussels on Saturday hoping to get "clarity" on President Donald Trump's controversial new steel and aluminium tariffs.
Ms Malmstrom said on Friday that she would seek clarity on the U.S. decision and was counting on an European Union exemption.
Malmstroem said Trump's announcement was "not crystal clear" and she would seek clarification when she saw US Trade Representative Robert Lighthizer in Brussels on Saturday for long-planned talks that are now a de facto crisis meeting. "The exact nature of the (EU) steps will be decided after a close analysis of the American measures."Separately, Germany's transatlantic coordinator, Juergen Hardt, told Reuters the US government should have exempted its European allies from punitive tariffs imposed against steel and aluminium imports that were primarily aimed at China".
Mr Seko called for calm-headed behaviour in the dispute.
The EU executive said it remained unclear how an exclusion would work.
"We are an ally, not a threat", he said, rejecting any hint that the bloc's exports threatened USA national security - Trump's justification for imposing the tariffs.
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In talks, the United States should not expect any European Union concessions to win an exemption, European Union officials said.
Canada and Mexico were given specific exemptions from the tariffs for an indefinite period while negotiations continue on the North American Free Trade Agreement. "Now we are talking about unilateral action against worldwide rules, and we want to sort it out before it really becomes a problem".
The duties of 25 percent on imported steel and 10 percent on aluminum have stung the EU, along with other major partners including Japan, and European Trade Commissioner Cecilia Malmstroem said earlier Washington had failed to clarify how its allies could be spared.
It has already started monitoring incoming metal flows to see whether a surge occurs.
Brussels is also looking at "safeguard" measures to protect its industry - restricting the bloc's imports of steel and aluminium to stop foreign supplies flooding the European market, which is allowed under World Trade Organization rules.
European steel and aluminium associations have warned that the US tariffs could cost their sectors thousands of jobs.