German Chancellor Angela Merkel, French President François Hollande, and Italian Prime Minister Matteo Renzi have agreed that no talks will be held with the United Kingdom on leaving the European Union until the British government invokes Article 50 of the EU’s main governing document, the Treaty of Lisbon.

“We are in agreement that Article 50 of the European treaties is very clear—a member state that wishes to leave the European Union has to notify the European Council,” Merkel said after a meeting in Berlin with Hollande and Renzi.

Article 50 stipulates that countries wishing to leave the EU must inform the European Council of their intentions to begin a process of exit negotiations that can last a maximum of two years. Once Article 50 is invoked, there is no turning back. But British Prime Minister David Cameron and leaders of the campaign to exit the EU in the U.K. have shown no urgency to do so, despite the Leave campaign’s victory in Thursday’s EU referendum.

On Friday, Cameron laid out a three-month timetable for preparations to begin exit negotiations, which he announced would take place under the leadership of a new prime minister. He reiterated this stance in a speech to Parliament on Monday. “I think it’s right not to trigger Article 50,” he told members, “because that starts a process that within two years has to result in an exit and it might be an unmanaged exit if it started too soon.”

But in their post-meeting comments, Merkel, Hollande, and Renzi urged Britain to expedite preparations to quell uncertainty and dismissed the idea that negotiations could happen without the invocation of Article 50. “Our responsibility is not to lose time in dealing with the question of the U.K.’s exit and the new questions for the 27 [other EU nations],” Hollande told the press.

The trio’s comments echoed statements made over the weekend after a separate meeting of the foreign ministers from the EU’s six founding states as well as comments made on Saturday by European Commission President Jean-Claude Juncker, who explicitly criticized Cameron’s three-month timetable in an interview. “Britons decided that they want to leave the European Union,” he said. “It doesn’t make any sense to wait until October.”

Read more from Slate on the Brexit vote.