After a meeting in Berlin, foreign ministers of the six founding member countries of the European Union sent a clear message to Britain to leave the union as soon as possible and to set the process for exit in motion. (Reuters)

Following the landmark vote in Britain to withdraw from the European Union, foreign ministers from the bloc’s six founding nations urged London on Saturday to move toward the exit door as “quickly as possible.”

Meeting in Berlin, the top diplomats of Germany, France, Italy, the Netherlands, Belgium and Luxembourg collectively called for fast follow-through on the stunning British decision, putting pressure on Prime Minister David Cameron, who has sought a slower pace of extraction.

On Friday, Cameron said he would step down after several months but has not immediately sought to trigger the European Union’s Article 50, which would set up a two-year negotiating period ending with withdrawal. Cameron indicated that he would leave the exit decisions to his successor.

But the top diplomats meeting Saturday suggested the European Union was not prepared to wait for domestic politics to play out in Britain, suggesting that Cameron would face intense pressure on Tuesday during a summit in Brussels of 28 national leaders and European officials.

“We start now,” French Foreign Minister Jean-Marc Ayrault told reporters. “We must be clear. The British people have decided after an initiative that was taken by Mr. Cameron. That was, is his responsibly.”

In a stunning victory for the "Leave" campaign, Britain has voted to exit the European Union. Here's what happens next. (Jason Aldag,Adam Taylor/The Washington Post)

German Foreign Minister Frank-Walter Steinmeier echoed calls for talks to start as “soon as possible.”

“We understand and respect the result and understand that Great Britain now concentrates on Great Britain,” Steinmeier said. But, he said, “this process should begin as soon as possible, so that we don’t end up in a long stalemate but are able to concentrate on the future of Europe and work on it.”

Jean Asselborn, foreign minister of Luxembourg, said the “problem” now is that only the British government and its parliament could activate Article 50. “Nobody in the European Union can force Article 50 on Britain. I hope this won’t turn into a cat-and-mouse game. . . . There must be clarity here. The people have spoken.”

Top E.U. officials and leaders have been scrambling to draft a blueprint for what has never before happened: the withdrawal of an E.U. member state. Some are calling for tough and speedy talks with Britain while others have been more mollifying, urging flexibility.

Steinmeier told reporters he was “confident” the remaining states would stick together, sending a “message that we won’t let anyone take Europe from us.” Earlier, he also sounded a conciliatory note toward Britain, telling ZDF television that Europe should “not go looking for revenge.”

The Saturday meeting came as governments from Dublin to Paris to Berlin confronted their worst-case scenarios. On Friday, top leaders of the union’s executive and legislative branches met in Brussels while E.U. ambassadors — all 28 of them, for now — convened in the afternoon in Luxembourg.

The rounds of diplomacy were laying the groundwork for a previously planned E.U. summit Tuesday, when the highest-level talks by national leaders will begin on how to handle what could be a painful, messy process of a British exit.

Yet many leaders, including the key foreign ministers meeting Saturday, have also conceded that the union needs to be respond to widespread public criticism and antipathy among European voters who think it has become too remote and too controlling of their lives.

On Saturday, Steinmeier told reporters that E.U. politicians needed to further consider “the expectations of the people.”