(Graffiti in a Tripoli market, January 17, 2012/Tom Heneghan)

Libya, preparing for elections in June, has banned parties based on religion, tribe or ethnicity, the government said on Wednesday, and a new Islamist party viewed as a leading contender signalled it would challenge the decision.

National Transitional Council spokesman Mohammed al-Harizy said the council passed the law governing the formation of political parties on Tuesday evening. “Parties are not allowed to be based on religion or ethnicity or tribe,” he told Reuters.

He did not make clear how this would affect a political party formed in March by Libya’s Muslim Brotherhood and other Islamists. The new party was expected to make a strong showing in the election, the first since last year’s overthrow of Muammar Gaddafi in a NATO-backed popular uprising.

The head of the Brotherhood’s Freedom and Development Party said the NTC needed to make it clearer what it meant by banning religious parties. He said this would cause controversy in conservative Libya, whose population of six million is made up almost entirely of Sunni Muslims.

“This kind of clause is only useful in countries where there exists many religions, not in Libya where most people are religious Muslims,” Sawan told Reuters.