If you look on the internet it is easy to find 10-day-old children

Rudi Tarneden, Unicef spokesman

Most of the children come from developing countries and are sold to couples in the developed world trying to get around tough adoption laws at home.

Many of them, it says, are willing to pay $20,000 or more for a baby.

Booming trade

At its press conference in Berlin, Unicef also voiced concern about the legality of adoptions from eastern Europe and Russia.

The Vietnamese Government has imprisoned people for selling babies

In the relatively poor central American country of Guatemala, selling babies is big business.

According to Unicef, the trade is worth an estimated $25m a year.

Some of the adoptions are considered legitimate, but many more are part of a thriving and unscrupulous adoption industry.

Rudi Tarneden, spokesman for Unicef Germany, says the international community needs to act now.

"This process is becoming more and more out of control and we see a problem that this inter-country adoption market is now through private channels," he said.

Unicef says the process is getting out of control

"If you look on the internet it is easy to find 10-day-old children and more and more couples from industrialised countries use this channel."

The problem does not just exist in central America.

Earlier this year, a court in Vietnam sentenced 12 people to prison for selling new-born babies to foreign couples abroad.

Eastern Europe

Unicef has also voiced concern about the legality of adoptions from eastern Europe, especially Russia.

How these children end up for sale varies.

Some are stolen, some are sold by their parents for money and some are willingly given up for hopes of a better life abroad.

Unicef says it does not have any exact figures for the illegal trade.

But it says the responsibility for tackling it lies not just with governments but with prospective parents themselves.