Language-divided Belgium faces a decisive week as a French-speaking leader Monday mooted a break-up ahead of a deadline set by the king to resume marathon talks to form a government.
"The situation is very serious," Elio Di Rupo, head of the Francophone Socialist Party, said in an interview in the daily Le Soir.
"If a political party really wants to show the federal state no longer works ... that it wants to step towards the detachment of Flanders, then I believe we must be 'honest' and organise a popular vote in Flanders," said Di Rupo.
"I don't think most Flemish people want independence," he added, referring to the country's 6.2 million Flemish-speaking majority, compared to 4.5 million French-speakers. "But if that were the reply, French-speakers would keep Belgium, made up of Brussels, Wallonia, and six (Brussels) districts."
Belgium, which plays host to pre-eminent world bodies NATO and the EU, has been rudderless since June elections, with leaders of the country's Flemish- and French-speaking communities so far failing to bridge differences and form a coalition government.
Following the collapse of the latest round of talks, King Albert II on Friday gave the head of the Flemish nationalist N-VA party, Bart De Wever, until Monday next week to bridge the rift in order to facilitate new talks to form a government.
But De Wever's party this weekend threatened to launch a parliamentary challenge against special voting and legal rights enjoyed since the 1960s by 130,000 French-speakers living in the Brussels suburbs, which are part of a Flemish region.
The threat has caused new tension ahead of the sovereign's October 18 deadline, with one French daily saying "We will keep Belgium" on its front page.
It was the first time Di Rupo had spoken in such detailed terms of a break-up of the country, in which the richer, Flemish-speaking north would separate from the capital Brussels and the French-speaking south.
Di Rupo's Socialists and De Wever's nationalist N-VA were the winners of the inconclusive June vote.
Jan Jambon, president of the N-VA's parliamentary group, said Sunday the party would introduce a measure to end what Flemish leaders see as "undeserved" special rights of French-speakers in the Bruxelles-Hal-Vilvorde (BHV) area if the political deadlock at the national level had not been broken by October 18.
Di Rupo reacted sharply, saying "We are not going to let ourselves be impressed by ultimatums. But if the end solution was a smaller country of French-speakers, comprising the capital, we can live this way too!", he said.
Last week De Wever broke off talks in frustration at the refusal of French-speaking parties to agree to the federal state devolving more tax-raising powers to the three regions, Flanders, Wallonia and Brussels.
Francophones fear their Wallonia region, already less wealthy than its northern neighbour Flanders, would become poorer under such a fiscal reform and warn it could lead to the break-up of Belgium.
Belgium, one of the EU's founding members, currently holds the rotating presidency of the 27-member bloc until December.