Swiss voters overwhelmingly approved a constitutional ban on minarets on Sunday, barring construction of the iconic mosque towers in a surprise vote that put Switzerland at the forefront of a European backlash against a growing Muslim population.

Muslim groups in Switzerland and abroad condemned the vote as biased and anti-Islamic. Business groups said the decision hurt Switzerland’s international standing and could damage relations with Muslim nations and investors who bank, travel and shop there.

“The Swiss have failed to give a clear signal for diversity, freedom of religion and human rights,” said Omar Al-Rawi, integration representative of the Islamic Denomination in Austria, which said its reaction was “grief and deep disappointment.”

Some 2.67 million people voted 57.5 to 42.5 per cent in favour of the referendum by the nationalist Swiss People’s Party, which labelled minarets as symbols of rising Muslim political power that could one day transform Switzerland into an Islamic nation. Voters in only four of 26 states opposed the initiative, granting the double approval that makes it part of the Swiss constitution.

Muslims comprise about 6 per cent of Switzerland’s 7.5 million people. The sponsors of the initiative said the growing Muslim population was straining the country “because Muslims don’t just practice religion. They increasingly make political and legal demands.”

The seven-member Cabinet that heads the Swiss government spoke out against the initiative but the government said it accepted the vote and would impose an immediate ban on minaret construction.