The 40-day exemption granted by Washington was like U.S. President Donald Trump putting "a gun to our head", complained French President Emmanuel Macron. The EU's trade chief demanded that the United States drop "artificial deadlines". Her boss, European Commission President Jean-Claude Juncker, said he saw achieving agreement in the dispute by May 1 as unrealistic.

Trump said on Thursday he would suspend tariffs for the EU, the United States' biggest trading partner, as well as Argentina, Australia, Brazil, Canada, Mexico and South Korea. The tariffs are suspended until May 1 as discussions continue.

In a joint statement, EU heads of state and government, meeting for a summit in Brussels, said the measures could not be justified on national security grounds - the basis cited by Washington - and that the exemption should be permanent.

"The European Council regrets the decision by the United States to impose import tariffs on steel and aluminum," they said. "Sector-wide protection in the U.S. is an inappropriate remedy for the real problems of overcapacity."

The leaders also said they supported steps taken by the European Commission to respond to the U.S. measures "as appropriate and in a proportionate manner".

Cecilia Malmstrom, the trade commissioner who negotiates on behalf of the 28 nations, said Europeans did not want to be penalized by actions prompted largely by accusations of Chinese dumping and said Washington and Brussels should be cooperating.

"The U.S. and EU should be tackling such issues together. We now look forward to pursuing a dialogue with the U.S. on trade issues of common concern, such as global steel overcapacity," she said on Twitter.

"These discussions between allies and partners should not be subject to artificial deadlines."

German industry, aware that Trump has warned he could raise duties on EU cars, welcomed the reprieve but said the threat of a trade war had not disappeared.

"We still have the threat of escalating global trade conflict. And U.s. President Donald Trump will demand a price for the tariff exclusion," Thilo Brodtman, head of Germany's VDMA engineering federation said in a statement.

German Chancellor Angela Merkel said Europe was trying to avoid a trade war in which everyone would lose.

European steelmakers group Eurofer said the danger to the EU market had not disappeared, with the exemption only temporary, and that the EU needed its own quotas or tariffs to stop steel otherwise bound for the United States from flooding into Europe.

Europe says it wants to avert a trade war but the European Commission has proposed a series of measures if the White House hits EU producers.

It would launch a challenge at the World Trade Organization, consider measures to prevent a surge of metal imports into Europe and impose import duties on U.S. products to "rebalance" EU-U.S. trade. Malmstrom said the EU was keeping its options open.

The counter-measures would include EU tariffs on U.S. orange juice, tobacco, bourbon and Harley-Davidson Inc motorcycles.

Austrian Chancellor Sebastian Kurz said the EU did not want a trade war but would respond "firmly" if the president took "the wrong decision".

Belgian Prime Minister Charles Michel underlined the irritation among some EU leaders at Trump's negotiating tactics.

"I have the impression that the U.S. leader wants to negotiate with the European Union by putting a gun to our head," Michel said, in an expression later echoed by Macron.

"That's a strange way to negotiate with an ally."

(Additional reporting by Georgina Prodhan in Frankfurt and Paul Carrel in Berlin; writing by Richard Lough; editing by Noah Barkin and Philip Blenkinsop)

By Richard Lough and Philip Blenkinsop