UPDATE 1-EU promises firm response to U.S. steel tariffs

(Adds comment from European steelmakers association Eurofer, background)

BRUSSELS, March 1 (Reuters) - The European Union said it would propose countermeasures within days in response to the United States' decision to impose hefty tariffs on steel and aluminium imports, which it called a "blatant intervention" to protect U.S. industry.

U.S. President Donald Trump announced on Thursday he would impose duties of 25 percent on imported steel and 10 percent on aluminium imports to shield U.S. producers.

"We strongly regret this step, which appears to represent a blatant intervention to protect U.S. domestic industry and not to be based on any national security justification," European Commission President Jean-Claude Juncker said in a statement.

"We will not sit idly while our industry is hit with unfair measures that put thousands of European jobs at risk ... The EU will react firmly and commensurately to defend our interests."

Juncker said that the Commission would put forward a proposal for WTO-compatible countermeasures against the United States in the next few days to rebalance the situation.

European steelmakers association Eurofer said a global tariff of 25 percent on steel imports meant the United States had chosen trade confrontation, rather than a quota that could have allowed allies to maintain their U.S. presence.

"From one day to the next, EU steel exports to the U.S. - which were at 5 million tonnes in 2017 - will be cut drastically by an estimated 50 percent or more," Eurofer Director Genereal Axel Eggert said in a statement.

He said he welcomed the Commission's announcement of appropriate and swift measures.

"The EU must not allow that the moderate recovery in our industry over the last year is now being destroyed by the EU's most important political ally," Eggert said. (Reporting by Alissa de Carbonnel zAdeCar and Philip Blenkinsop Editing by Peter Graff and Susan Fenton)