The United Nations High Commissioner for Refugees, Ruud Lubbers, has condemned a proposal by the right-wing Swiss People's Party to clamp down on asylum seekers.
Switzerland is later this month to vote on the party's initiative, which would impose tough new restrictions on asylum seekers.
The People's Party proposal would prohibit asylum seekers from filing an application in Switzerland if they had passed through a so-called "safe" country first.
Since Switzerland is surrounded by "safe" countries, the effect would be to limit substantially the number of applications.
The UNHCR, whose headquarters are in Geneva, has described the campaign as "misleading", saying it could lead to some of the toughest asylum restrictions seen in any industrialised nation.
"If the Swiss people vote 'yes' to this initiative, it will effectively mean that any refugee arriving in Switzerland by land will be rejected straightaway, however well founded their request for asylum," said Lubbers.
"Since the vast majority of refugees reach Switzerland in this way, we will have a country, Switzerland, whose doors will more or less be closed to people fleeing persecution, even people who have suffered or witnessed atrocities, massacres or torture."
The People's Party dismissed the UNHCR's comments, and called on the government to lodge an official protest against "the UNHCR's interference in our affairs".
"It's intolerable that the UN wants to influence the vote in Switzerland. We are a free country and we want to take decisions ourselves," spokesman Yves Bichsel told swissinfo.
The Swiss government, which is opposed to the People's Party proposal, said the UNHCR was not just any organisation and was fully entitled to comment on the initiative.
Raymond Hall, head of the UNHCR's European office, says that if the proposal is adopted, the burden will fall on neighbouring countries to prove whether asylum seekers are genuine.
According to Hall, Switzerland's neighbours already have to cope with existing asylum demands and will be badly placed to deal with the fallout from such radical and unilateral action by the Swiss.
"The initiative risks creating more problems than it will resolve," he said.
The agency said it recognised that there was abuse of Switzerland's asylum system, in common with many other western European countries, and it supported "serious efforts" to tackle the problem.
However, it maintained that such measures should not be to the detriment of genuine refugees seeking sanctuary in Switzerland.
"The initiative and the campaign which accompanies it identifies the problems but doesn't propose realistic ways of resolving them," said Hall. "Moreover, it clearly goes against the spirit of international law."
Hall also said the initiative ran counter to Switzerland's strong humanitarian tradition.
The Swiss Peoples' Party responded by saying that this argument was merely being used to scare voters, wary of damaging Switzerland's image abroad.
"I'm sure that other countries will understand that Switzerland has to do something about this problem with asylum seekers," Bichsel said.
Bichsel also refuted the UNHCR's criticism that the initiative was being presented misleadingly as a means of combating drug trafficking and crime in Switzerland.
"About 70 to 80 per cent of drug traffickers caught by the police in Switzerland are refugees and I don't see why the UNHCR doesn't want to acknowlege this," he said.
"It's obvious that there is a problem which has to be resolved."
UNHCR condemns asylum proposal
The Swiss vote on November 24 on whether to adopt the People's Party proposal.
A recent poll showed that 57 per cent of voters are in favour of stricter asylum laws.