Louis Freeh called for greater coordination

His comments came at a conference of interior ministers from 12 Central and Eastern European countries in the Romanian capital Bucharest.

The conference is aimed at discussing ways to fight human trafficking, which is becoming increasingly widespread and involving growing numbers of Eastern European women and children in prostitution.

Mr Freeh called the trade a modern-day form of slavery.

Modern-day slavery

Addressing the delegates, Mr Freeh added his voice to calls for greater unity in fighting the multi-billion dollar trade.

"We have to direct our efforts to protect the most vulnerable ... we will only succeed if we collaborate police officer to police officer, government to government," he said.

But correspondents say the situation is complicated by the fact that in many countries, trafficking is not specifically defined as a crime.

We will only succeed if we collaborate police officer to police officer

Louis Freeh, FBI director

The conference host - Romania - is one of the countries used as a marketplace for women from further east.

A recent investigation in Bosnia suggested that women from Moldova were bought and sold in the western Romanian city of Timisoara.

In the Moldovan capital, Chisinau, a string of travel agencies were recently closed by the police, after they were accused of being involved in prostitution rackets.

But absence of legislation and lack of witness protection have so far made it hard to make successful prosecutions.

Poorly paid border officials in several countries are often bribed to turn a blind eye to the trade.