Source: compiled by the GT Graphics: GT

The European Parliament's chief called Sunday for British Prime Minister David Cameron to begin formal proceedings to leave the European Union at a summit this week.

Martin Schulz told German newspaper Bild am Sonntag that a period of limbo over Brexit would "lead to even more insecurity and thus endanger jobs."

"Hesitating simply to accommodate the party tactics of the British Conservatives hurts everyone," he said. "That is why we expect the British government to now deliver. The summit on Tuesday is the right time."

The four biggest groups in the European Parliament have drawn up a draft resolution calling for Cameron to get the Brexit ball rolling on Tuesday, Germany's Frankfurter Allgemeine Sonntagszeitung reported.

This is crucial, the groups wrote, "to avoid damaging uncertainty for all and to preserve the integrity of the union."

They added that "no new relationship of whatever kind between the United Kingdom and the EU can be agreed before [Britain's] exit accord has been completed."

On Friday, in the wake of the shocking referendum outcome favoring Britain leaving the EU, Cameron said he would resign his office by October and leave the Brexit negotiations to his successor.

To begin the withdrawal process, Britain must invoke Article 50 of the EU's Lisbon Treaty. The first step is to inform the European Council of member states, which sets the clock ticking on a two-year timetable of negotiations.

The EU will hold a summit on Tuesday and Wednesday to discuss the fallout from the British vote, while the European Parliament will also hold a special session.

Foreign ministers from the EU's six founding states meeting in Berlin on Saturday urged Britain to begin the exit process "as soon as possible."

Chancellor Angela Merkel, however, was more cautious, saying it was up to Britain to decide when to begin withdrawal proceedings, although they should not "drag on forever."

"There is no reason to be nasty in the negotiations. We have to follow the rules of the game," she said Saturday. Her chief of staff, Peter Altmaier, told German public radio that he did not believe Cameron would start the Brexit process on Tuesday.

"I have no indication that will happen. I tend to think that the application will be filed in the coming weeks or months, possibly only by a new government," he said.