The United Nations urged European countries not to react to Friday's attacks in Paris by rejecting or blaming refugees, the vast majority of whom were fleeing persecution or conflict.
"We are concerned about reactions by some states to end the programmes being put in place, backtracking from commitments made to manage the refugee crisis (i.e. relocation), or proposing the erection of more barriers," UNHCR's chief spokeswoman Melissa Fleming said.
"We are deeply disturbed by language that demonises refugees as a group. This is dangerous as it will contribute to xenophobia and fear."
She said UNHCR was deeply concerned by the "yet unconfirmed" report that one of the attackers in the Paris attack may have entered Europe as part of the influx of refugees.
The best response would be to immediately improve arrival processing in Greece and Italy and implement the European Union's plan to relocate 160,000 refugees.
"We believe that if this had been done from the beginning we never would have seen these images on our screens of people on the march through Europe. It wouldn't have solved it but it would have gone a long way to managing it."
Asked if UNHCR had warned of the risk that the badly-managed refugee influx could allow militants to slip into Europe, Fleming said UNHCR had warned in general terms of the importance of proper screening.
U.N. human rights spokesman Rupert Colville said the biggest group of people to suffer at the hands of Islamic State militants, also known as ISIL, were Muslims in Syria and Iraq.
"If this attack is allowed to feed discrimination and prejudice it will be playing straight into the hands of ISIL," he said. "Are we going to play their game for them?
"Demonising already marginalised communities is clearly a stupid way to go."
Joel Millman, a spokesman for the International Organization for Migration, said that out of about 1.1 million arrivals in Europe in the past few years, at most a handful had names that raised questions with respect to possible links to extremism.
IOM figures show that 832,193 migrants and refugees have arrived in EU countries across the Mediterranean Sea so far this year, and at least 3,505 have died in the attempt.
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