BRUSSELS (Reuters) - A growing debate about the potential division of Belgium has led to a surge in sales of Belgian flags as opponents of separatism seek to display their patriotism.

Belgians are accustomed to flying the black-yellow-red tricolor on the king's birthday, July 21, but in recent weeks far more flags have been hung from windows and balconies, particularly in the capital, Brussels.

"In the last couple of weeks sales have tripled. I'd say we've sold two, three, four hundred flags and it's private individuals we are seeing coming in," said Walter Michiels, who owns a business selling flags in Brussels.

Kristel Cartentier of flag and print business Artemis said she too had noted a tripling of sales.

"People are coming in saying they want to show their support for Belgian unity," she said.

The national anthem, the Brabanconne, has also become the most downloaded tune for use as a mobile phone ring -- among French-speaking Belgians.

However, the flag-waving is not a countrywide phenomenon. It has barely taken off in the Dutch-speaking region, Flanders, where support for independence is strong.

Talk of division has grown as Flemish and Francophone parties have failed to form a coalition government 110 days since June 10 federal elections.

The Flemish Christian Democrats emerged as clear winners of the public vote, but their key demand to devolve more powers has met with stern opposition from Francophone parties.

The impasse has prompted media to speculate the 177-year-old nation might be better off breaking apart.

Recent polls show that a sizeable minority, at least 40 percent, of Flemish want Belgium to split, against fewer than 10 percent of French-speakers.

However, optimism has grown in recent days that the political crisis may be coming to an end as Flemish and Francophone political leaders have renewed negotiations and spoken more optimistically about forming a coalition.