Luxembourg (CNN) British Prime Minister Boris Johnson was forced to abandon a press conference with his counterpart in Luxembourg to avoid anti-Brexit protesters, in an extraordinary diplomatic dust-up between the two nations.

Bettel used the event to excoriate Johnson. He said the Brexit process had turned into a "nightmare" and that the UK had failed to present alternative proposals to the deal it had negotiated, but now rejects. "He holds the future of all UK citizens," said an impassioned Bettel, gesturing at the empty podium by his side. "It's his responsibility. Your people, our people count on you."

As Bettel spoke, a small but noisy crowd, many of whom were British nationals living in Luxembourg, clapped and cheered.

A rocky day

Johnson was in Luxembourg for his first face-to-face Brexit talks with European Commission President Jean-Claude Juncker. It was bumpy from the start -- the British Prime Minister was booed as he arrived at the restaurant where the talks were being held.

Meanwhile, crowds were already gathering outside Luxembourg's government buildings, where the meeting with Bettel was scheduled. The British government source said officials requested an indoor location for the post-meeting media briefing in order to avoid the chants of protesters.

Xavier Bettel addresses the meida next to an empty lectern intended for British Prime Minister Boris Johnson.

The decision to go ahead with the press conference against the wishes of British officials was a pointed move on the part of Bettel. Typically, host nations go to great lengths to avoid humiliating allies in this way.

In his remarks, Bettel delivered a thinly veiled rebuke to comments by Johnson on Sunday, who described breaking free of the EU's "manacles" in the manner of Marvel superhero the Hulk. Bettel said Brexit was "too serious a matter to speak about actors and a script."

Brexit was not the choice of the EU but that of the UK's Conservative government, Bettel said. "You can't hold our future hostage for party political gains," he said, adding: "I repeat this Brexit is not my choice."

Johnson admits avoiding protests

Speaking to UK media away from the protestors, Johnson gave his reasons for canceling the press conference. "I don't think it would've been fair to the prime minister of Luxembourg," he said. "I think there were clearly going to be a lot of noise and I think our points might've been drowned out."

Johnson admitted Brexit negotiations would have to be accelerated, and that the EU must make "movement" over the Irish backstop but added that there was "just the right amount of time" to do a deal.

Johnson's spokesperson had earlier said that talks with Juncker were "constructive" and that the UK PM had proposed an alternative solution to the Irish backstop -- a part of the withdrawal agreement negotiated by Johnson's predecessor, Theresa May.

But the British proposals remain unclear and Juncker said the EU was still waiting to hear of a workable alternative to the backstop.

In a statement after the talks, Juncker said the aim of the meeting was to "take stock" of the ongoing Brexit negotiations and to discuss the "next steps."

European Commission President Jean-Claude Juncker, right, poses with Boris Johnson before meeting at a restaurant in Luxembourg.

The Commission President said it was "the UK's responsibility to come forward with legally operational solutions that are compatible with the Withdrawal Agreement," adding that "such proposals have not yet been made."

"The Commission will remain available to work 24/7," Juncker's statement continued. "The EU27 remain united."

UK says 'ignore the noise'

Downing Street said Johnson had used the meeting to repeat his assertion that he will not request an extension to the October 31 deadline for Britain's departure from the European Union.

"The leaders agreed that the discussions needed to intensify and that meetings would soon take place on a daily basis," Johnson's spokesperson said.

"It was agreed that talks should also take place at a political level between Michel Barnier and the Brexit Secretary, and conversations would also continue between President Juncker and the Prime Minister," the PM's spokesperson added.

A UK government source said that despite the bad headlines from the abandoned press conference, the day had been constructive. "If you ignore the noise, let's look at what happened during the PM's visit. He had a good meeting with Jean Claude-Juncker where they agreed to intensify talks. We need to start accelerating talks if we're going to make further progress."

"This is on the back of positive meeting in Dublin last week. If EU are prepared to move on the backstop -- rejected three times by Parliament -- then we can see the rough shape of a deal. We are working in a positive and determined way to get a new deal."

The backstop plan, aimed at avoiding a hard border between Northern Ireland and the Republic of Ireland, is designed to come into force if the complex issue of the Irish border has not been resolved by the time the Brexit transition period -- which keeps the UK in a customs union with the EU -- ends in 2020.

The Downing Street statement added that Johnson "reconfirmed his commitment" to the 1998 Good Friday agreement, which helped bring about peace in Northern Ireland after decades of sectarian violence, and that he still had a "determination to reach a deal with the backstop removed."