For the third time, Swiss voters have turned down a proposal to make it easier for foreigners to become naturalized Swiss citizens.

Switzerland has some of the strictest naturalization and citizenship laws in the world and on Sunday nearly 57 per cent of Swiss voters said they want to keep it that way, rejecting the government's efforts to bring Switzerland's citizenship requirements in line with other Western European countries.

In large part it was the traditionally conservative German-speaking cantons that stopped the measure. They voted as a bloc to prevent third generation foreigners, born in Switzerland, from automatically becoming citizens.

An advertisement of the Swiss People's Party against the easing of naturalization laws. The poster reads:"Naturalization for the Masses?" (AP Photo/Keystone)

Foreigners currently number 1.5 million, or about 20 per cent of the Swiss population. One in four of those were born in Switzerland.

People in the more liberal French-speaking part of the country voted overwhelmingly in favor of the constitutional changes.

The result only served to highlight the deep political and social divisions which exist between these two linguistic groups. Tempers were short in the aftermath of the vote as supporters and opponents of the initiative debated the issue.

Supporters of the legislation accused the right wing Swiss People's Party of having run a dirty campaign, frightening the population by depicting foreigners as terrorists, pointing to a campaign poster which showing Osama bin Laden's photo on a Swiss ID card.

Another controversial newspaper advertisement claimed that Muslims would eventually become a majority in Switzerland if the citizenship rules were eased. Opponents said they were simply explaining that the Muslim population was doubling every 10 years.

Swiss Justice Minister Christoph Blocher said the government would accept the results and that there were no plans to present new proposals.