WASHINGTON (Reuters) - President Donald Trump on Friday blasted the European Union for its use of trade barriers and revived his threat to impose U.S. tariffs on European automobiles if he does not see progress in stalled negotiations between the longstanding partners.

Trump made the comments shortly after signing a deal to sell more U.S. beef to Europe, an event at which he startled participants by joking that his administration was working “on a 25% tariff on all Mercedes-Benz and BMWs coming into our nation”. He then said he only kidding.

“The EU has tremendous barriers to us,” Trump told reporters later at the White House. “They’re very, very difficult.”

Trump said the threat of auto tariffs may have helped move the EU toward accepting the beef deal, but auto tariffs remain an option.

“Auto tariffs are never off the table,” Trump said. “If I don’t get what we want, I’ll put auto tariffs. ... If I don’t get what I want, I’ll have no choice but maybe to do that. But so far they’ve been very good.”

EU officials have said they are eager to work with the United States to reform the World Trade Organization (WTO) and rein in China’s behavior on world markets, but would retaliate if Washington makes good on its threat to raise car tariffs.

Sabine Weyand, the European Commission’s director general of trade, last month said Brussels would not be bullied by the threat of car tariffs, which it views as illegal under WTO rules.

Negotiators for Brussels and Washington have been meeting since Trump and then-European Commission President Jean-Claude Juncker agreed to ease trade tensions last year, but have made little progress and remain at odds over the scope of the talks.

The United States wants agricultural products included in a broader trade deal, but the EU has said its mandate from member countries does not include that area.

Germany’s coordinator for transatlantic ties, Peter Beyer, said the beef agreement shows progress is possible when both sides work together constructively, and called for fresh efforts to reach a broader trade deal.

“I urge the United States to now, finally, begin serious negotiations to reach an industrial tariff agreement” he said in a statement.