ZURICH (Reuters) - The Swiss diplomat who helped negotiate a United Nations migration pact has defended the accord against mounting criticism, saying it helps small countries like Switzerland defend their interests.

The Global Compact for Safe, Orderly and Regular Migration was instigated after the migration crisis in Europe in 2015, which saw the biggest influx of refugees and migrants since World War Two. The crisis strained resources and triggered fear of foreigners and nationalist tensions.

It was approved in July by all 193 member nations except the United States, which backed out last year.

The comments from Pietro Mona, Swiss ambassador in charge of development and migration policy, come amid growing opposition to the accord, with Hungary’s right-wing government saying it will not sign the final document at a ceremony in Morocco in December.

Austria pulled out too last month, and the prime ministers of Poland and the Czech Republic have cast doubt on their countries’ joining.

Mona said Swiss negotiators deserved credit for having the pact become the first international document to set out states’ obligation to cooperate in taking back citizens.

“The migration pact gives us an additional instrument that helps us negotiate repatriation agreements, for instance with countries like Eritrea,” he said in an interview with the Blick tabloid, published on Monday.

After some hesitation, the Swiss government said last month it would sign the compact while clarifying its position on detaining minors from the age of 15 pending deportation, which Swiss law allows but the non-binding U.N. pact discourages.

Since then, committees in both houses of parliament have called for delaying the Swiss signature and giving parliament -- and perhaps voters in a referendum -- the chance to decide the matter.

Some politicians, especially from the right, complain that the pact could blur the line between legal and illegal migration and undermine countries’ sovereignty.

U.N. Special Representative for International Migration Louise Arbour has called moves to shun the accord regrettable and mistaken and said the compact simply aimed to improve the management of cross-border movements of people.

The U.N. pact addresses issues such as how to protect people who migrate, how to integrate them into new countries and how to return them to their home countries.

The United Nations has hailed it as a historic and comprehensive pact that could serve as a basis for future policies.