Juncker says he will "bring forward in the next few days a proposal for WTO-compatible countermeasures against the U.S. | Emmanuel Dunand/AFP via Getty Images EU vows to hit back against Trump in trade war US president had announced tariffs of 25 percent on steel and 10 percent on aluminum.

European Commission President Jean-Claude Juncker said today he would "bring forward in the next few days a proposal for WTO-compatible countermeasures against the U.S." to hit back against steel and aluminum tariffs announced by U.S. President Donald Trump.

The Commission confirmed Trump's announced tariffs of 25 percent on steel and 10 percent on aluminum would affect EU exports. "Instead of providing a solution, this move can only aggravate matters," Juncker said in a statement. "The EU will react firmly and commensurately to defend our interests."

EU trade chief Cecilia Malmström added the EU would impose safeguard measures on top of any retaliation against the U.S. These trade defenses would help the EU manage diverted flows of steel that had initially been intended for the U.S.

"These U.S. measures will have a negative impact on transatlantic relations and on global markets... The Commission will monitor market developments and if necessary will propose WTO-compatible safeguard action to preserve the stability of the EU market."

In a strong allusion to China, Malmström said that "global overcapacity caused by non-market based production" was a "problem," but criticized Trump's response. "This can only be addressed at the source and by working with the key countries involved. This go-it-alone action by the US will not help."