New Delhi, Dec. 11 -- As sympathy for immigrants erodes around the world, European nations agreed Wednesday to consider changes that rights advocates say would weaken migrant protections that have underpinned European law since World War II.

The consensus coalesced as mainstream political parties across Europe have adopted tougher migration policies as a way to blunt the momentum of far-right politicians exploiting discontent over immigration, even though illegal border crossings are actually falling.

Members of the 46 countries that make up the Council of Europe acknowledged "challenges" posed by migration while reaffirming their respect for the European Convention on Human Rights and the European Court of Human Rights, the council's s...