The Latest: EU's Tusk expresses "cautious optimism" on trade

The Latest on the reaction to President Donald Trump's proposal to put tariffs on steel and aluminum (all times local):

6:05 p.m.

European Union Council President Donald Tusk says he has "cautious optimism" that a trade war between the EU and the United States over steel and aluminum tariffs can be avoided.

Tusk said the EU's trade chief, Cecilia Malmstrom, was having good talks in Washington, where she is asking that the EU be exempted from the planned tariffs.

Tusk said in Brussels: "I use intentionally this term 'cautious optimism' but I have good reasons to believe that Commissioner Malmstrom will be even more effective than we expected two or three days ago."

He added that "everything will be clear tomorrow" when the 28 EU leaders will open a two-day summit where the trade differences with Washington will be high on the agenda.

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4:40 p.m.

German Chancellor Angela Merkel is backing talks aimed at averting U.S. steel and aluminum tariffs that she believes are illegal, but says Europe will retaliate in an "unambiguous" way if it has to.

The European Union is seeking an exemption from the tariffs for the 28-nation bloc. President Donald Trump's tariffs of 25 percent on imported steel and 10 percent on aluminum take effect Friday, but he has temporarily exempted Canada and Mexico.

Merkel told the German parliament Wednesday: "We will ... of course continue to back talks but if necessary take unambiguous counter-measures."

EU leaders are to discuss the issue at a summit Thursday. Merkel said: "We believe these tariffs are illegal, we think they are harmful ... but we must of course await developments."