A ban on the construction of minarets would breach Switzerland's obligations to uphold freedom of religion, Amnesty International said ahead of a referendum next Sunday on a constitutional amendment.

The proposal, which was initiated by members of two Swiss parties, will ask Swiss voters if they wish to add the sentence "The construction of minarets is forbidden" to Article 72 of the Constitution.

"Contrary to the claims of the initiators of the referendum, a general prohibition of the construction of minarets would violate the right of Muslims in Switzerland to manifest their religion," said Nicola Duckworth, Europe and Central Asia Programme Director at Amnesty International.

"A ban on the construction of minarets while, for example, allowing those of church spires would constitute discrimination on the basis of religion."

The initiators of the referendum claim that the construction of minarets is not protected by the freedom of religion as they have "no religious significance". They assert that minarets are "symbols of a religious-political claim to power and dominance which threatens - in the name of alleged freedom of religion - the constitutional rights of others."

Islam is the second largest religion in Switzerland after Christianity, and Muslims make up over four per cent of the country's population.

There are hundreds of places of worship (mostly in commercial buildings or private residences) in the country but only four minarets have been built.

The Swiss government and all the other major political parties are recommending a "no" vote.

Local Christian, Jewish and Muslim leaders have also joined forces to reject a ban on minarets.

They say that the referendum also poses a threat to peaceful relations between religions and inhibits the integration efforts of Muslims in Switzerland.

"While there may be legitimate reasons for measures which might in individual cases interfere with the construction of minarets, there is no legitimate public policy justification for a general prohibition on their construction," Nicola Duckworth said.

"A change in the constitution which would provide for the blanket ban on the construction of minarets must be soundly rejected. Such a move is important as it will reinforce the equality of rights for all people living in Switzerland."