King Albert II accepted Di Rupo's resignation and nominated one representative of each linguistic community – the Francophone speaker of the lower house of parliament, Andre Flahaut of the Socialist Party, and the speaker of the Senate, Danny Pieters of the Flemish separatist party N-VA – to lead mediation efforts to restart coalition talks.
Bart De Wever, leader of the Flemish separatist N-VA party, who emerged as the largest political force in Flanders after general elections in June, said there was not enough agreement on key issues.
The future of the Belgian capital Brussels, which plays host to the EU institutions, appears to be one of the main stumbling blocks standing in the way of forming a new government.
Belgium currently holds the rotating presidency of the EU.
The redefinition of the electoral boundaries around the city has plagued national politics since 2007, with Flemish politicians keen to recall that the Belgian capital is located on its side of the 'linguistic border'.
On Sunday, thousands of Flemish separatists took part in an annual demonstration, which consists of symbolically encircling Brussels by bike to remind locals that they are surrounded by Flanders.
Walloon politicians, on the other hand, stress the bilingual status of the city and are quick to point out that over 80% of its population is French-speaking. During the negotiations, they asked for more financing for Brussels and an extension of its boundaries to connect it with Wallonia to the south.
But these demands were rejected by De Wever. "Dramatising the situation is not helpful. Politicians must show their sense of responsibility," he said.
Meanwhile, Laurette Onkelinx, a Socialist Party leader, warned on Sunday that citizens should "get ready for the break-up of Belgium".
"When I look at the letters I receive, loads of people think it's possible. [Our] politicians have to be prepared," said Onkelinx, who is federal minister for health and social affairs in Belgium's caretaker government.
