EU leaders said Friday they would negotiate with the U.S. to resolve trade disputes, but warned they would not tolerate bullying — or any bull — from Donald Trump.

The U.S. president late Thursday granted the EU an exemption from punitive steel and aluminum tariffs that he has slapped on other countries, but he also set an expiration date for that exemption of May 1, which European leaders said did not leave enough time to reach a deal, and amounted to a threat.

“We can talk about anything with a friendly country," said French President Emmanuel Macron, who has developed arguably the best personal relationship with Trump among European leaders.

"But," Macron warned pointedly: "We don’t talk about anything in principle when it is with a gun to the temple."

EU leaders at a summit in Brussels, united by the scale the problems on their agenda, which included Russia as well as Trump, said they were hopeful a deal could be reached. But there was clear frustration with the U.S. president's evidently limited grasp of complex trade issues, his allegations of unfair practices (which the EU disputes) and the overall tumult and unpredictability emanating from Washington.

The EU has developed an arsenal of retaliatory measures targeting American goods in politically sensitive states.

Following a pattern set by other disagreements with Trump — over his withdrawal from the Paris climate change accords; his criticism of the Iran nuclear deal; and moving the U.S. Embassy in Israel to Jerusalem from Tel Aviv, which the EU opposed — European leaders tried to dial down the tensio to avoid inciting the combustible American president.

Trump upended the EU leaders' quarterly summit on Thursday with cryptic comments that left Brussels wondering if indeed it had been granted the promised exemption to his tariffs.

Discussion among the 28 leaders of a potential trade war — and the EU's battle plan for retaliation — was pushed back twice on the summit agenda, first from the Thursday afternoon to dinner, and then from Thursday evening to Friday, because of uncertainty in Washington. Trump held a news conference where he slapped new penalties on China — which sent U.S. markets into a tailspin — talked about "negotiations" beginning with the EU and repeated his complaints about unfair trade practices by Europe. But he never made clear an exemption had been granted.

That clarity came shortly before midnight Brussels time and received a mixed reception. Officials were glad to be granted an exemption, meaning the EU fared better than other allies such as Japan, but European leaders interpreted the May 1 expiration date as a threat.

Belgian Prime Minister Charles Michel was the first to use the gunpoint imagery. "This is maybe also a way to exert a strong pressure on the European Union and to start a kind of negotiation with a type of revolver at our head," Michel said as he arrived at the summit Friday.

In the European Council's formal conclusions, leaders once again rebuked Trump over the tariffs, which they assert violate World Trade Organization rules and cannot be justified, as Trump has claimed, by national security imperatives.

"The European Council regrets the decision by the United States to impose import tariffs on steel and aluminum. These measures cannot be justified on the grounds of national security, and sector-wide protection in the U.S. is an inappropriate remedy for the real problems of overcapacity, on which the EU already has offered the U.S. its full cooperation."

The leaders also reiterated their right to respond if Trump ever imposes the tariffs. The EU has developed an arsenal of retaliatory measures targeting American goods in politically sensitive states, including Kentucky bourbon, made in the home state of the Republican Senate majority leader, Mitch McConnell, and Harley Davidson motor bikes, made in Wisconsin, the home of the Republican house speaker, Paul Ryan.

At the summit's closing news conference, European Commission President Jean-Claude Juncker said he was happy Trump finally seemed to understand that the EU negotiates trade policy as a 28-member bloc.

"What the president was saying yesterday is recognizing that the European Union is an entity," Juncker said, noting the granting of a temporary exemption. "It cannot be divided into 28 parts. That's the good part of the news."

"We won’t show any weakness in any sector, in any country" — Emmanuel Macron

"The bad part," Juncker added, was the May 1 deadline, which he described as "highly impossible."

"It doesn't seem to me that this date is a very realistic one given the broad issues we have to discuss with the U.S.," he added.

Juncker also noted Trump's waffling. "He didn't take a decision," Juncker said. "He was deciding yesterday to suspend the measures he had imagined as far as the trade relations with the European Union are concerned."

European leaders were adamant they will not be bullied by Trump. "We won’t show any weakness in any sector, in any country," Macron said at a joint news conference with German Chancellor Angela Merkel.

Trump's tariffs and the $50 billion in penalties against China that he announced on Thursday reverberated across global markets and amounted to a major distraction at the EU summit, which was already confronting tough issues, including how to respond to Russia's alleged use of a nerve agent in the U.K.

One senior EU official said the menu of hard topics at the summit reminded EU leaders of their stature, and gave them confidence to stand up to Trump. "It was on the big issues," the official said. "They discussed Russia, Turkey, trade, America — without exaggerating, yesterday night was a moment where European leaders understand that all together they are a superpower themselves."