The EU is bracing itself for a trade war with the US, after Donald Trump’s administration signalled to Brussels that it would not prolong the exemption granted to European steel and aluminium importers from its punitive tariffs.

Cecilia Malmström, the European commissioner for trade, said that she expected the US commerce secretary, Wilbur Ross, to make a recommendation to the White House in the coming days, but that the final decision would be taken by the president.

A temporary exemption EU companies enjoy from a 25% tariff on steel and 10% tariff on aluminium brought in by Trump is due to come to an end on 1 June.

At a summit in the Bulgarian capital, Sofia, last week, EU leaders agreed to offer an increase in the amount of natural gas the US can import to Europe, reciprocal access for industrial products, including cars, and discussions on World Trade Organisation reform, if the White House was to lift the threat of tariffs.

Malmström said: “Is this going to be enough? I am not sure, frankly.

“There have been signals from the US that the exemptions will not be prolonged so either they will be imposed on us 1 June or there will other sorts of limiting measure … We have to prepare for different scenarios.”

Speaking after a meeting of trade ministers in Brussels on Tuesday, Malmström said she was in twice-weekly contact with Ross, and trusted him to be honest with her about his advice to the president.

Should tariffs be imposed on EU firms, the European commission president, Jean-Claude Juncker, has threatened to slap tariffs on Harley-Davidson motorbikes, bourbon and bluejeans, among other US products.

The 28 member states are, however, fractured over how to deal with Trump, whose tactics were described by Donald Tusk, the European council president, as being that of “capricious assertiveness”.

Germany, which has the most to lose from tariffs, has argued for a patient and generous response to the US’s threats.

The Netherlands and France have sought a tougher line, with the French president, Emmanuel Macron, describing Trump’s behaviour as a threat to EU sovereignty.

France’s trade minister, Jean-Baptiste Lemoyne, said: “We are allies but we are not vassals.”

However, Peter Altmaier, Germany’s finance minister, warned of the risks in tackling Trump head on.

He said: “With an escalation not only on steel, but also other products, and also with regard to problems with Iran, Russia, we risk a lot more than just economic repercussions.

“Whether the result will be positive, no one can say, but we lose if we don’t at least try. I remain optimistic that a solution can be found if both sides are interested in it and if both sides are prepared to move in the right direction.”

Luxembourg’s foreign minister, Jean Asselborn, suggested it would take a more generous offer from Brussels to convince the US to lift the threat of tariffs.

He said: “I think that on June 1 we will have another deadlock. Perhaps we will take a step forward in terms of what we can offer the Americans.”