At least 10,000 refugee children who travelled unaccompanied to Europe this year have disappeared without a trace, a spokesman for the European Union's law enforcement agency told dpa on Sunday.
"This does not mean that something has happened to all of them," the Europol spokesman said in the Hague. "Some of the children could in fact be staying with relatives."
"But it means that, at the very least, these children are potentially in danger," he added.
The 10,000-figure is "a modest estimate" covering the past 18-24 months, according to the spokesman. In Italy alone, local authorities have noted that around 5,000 youngsters among the recent influx of migrants and refugees are missing. In Sweden, the figure has reached 1,000.
The spokesman confirmed earlier comments from Europol chief of staff Brian Donald, who told British newspaper the Guardian that there was proof that some of the children among the missing had been sexually abused.
Donald said that large numbers of criminals had been imprisoned in Germany and Hungary for exploiting migrants and refugees, and spoke of a criminal "infrastructure" linked to both smuggling and sexual abuse.
"These children can become victims of abuse. And we ask our colleagues [in Europe] to be clear on the fact that this could happen," the crime agency's spokesman said.
Europol said that human trafficking circles, which profit from the ongoing humanitarian crisis by smuggling desperate people across dangerous land and sea routes, are now also trying to entrap people into slavery and prostitution.