The European Union says traffickers are taking advantage of Europe's migrant crisis to target certain types of people, often for sexual exploitation, with children and Nigerian girls and women among the most vulnerable.

An EU report into trafficking released Thursday said that crime gangs focus on children because they are easy to recruit and replace, with young migrants more exposed as they often travel long distances alone. The report also noted "a worryingly sharp increase in Nigerian woman and girls leaving Libya" has been seen.

The report says from January to September 2015, more than 4,370 Nigerian women and girls headed for Europe, compared to 1,008 the previous year. The International Organization for Migration says around 80 percent of them could be victims of trafficking.