"The conflict you have is quite clearly going to be a major factor in increasing vulnerability of some of the country's young people," Gary Lewis, representative of the UN Office for Drugs and Crime in South Asia, told Reuters.

"Migration is the key in which traffickers and traffic victims meet," Lewis said after a briefing in Colombo.

Sri Lanka, a developing nation of 20 million, has one of the lowest incidences of people smuggling in Asia, despite the ongoing conflict which has claimed 70,000 lives.

Lewis's office estimates at least 150,000 people are trafficked within South Asia each year, led by India and followed by Nepal, Bangladesh and Pakistan.

But with fighting intensifying between government troops and the rebels, the UN's refugee agency UNHCR says around 188,000 Sri Lankans have been forced from their homes since April 2006.

There are also tens of thousands of others living long-term in internal refugee camps after two-and-a-half decades of war, many in rudimentary conditions in tents.

"As soon as you disrupt a child from their home environment, there is movement and there is lack of physical contact with those who love and care for them," said Lewis, referring to children living in what were supposed to be temporary tent camps.

"You are going to get increased vulnerability on trafficking and also children being abused," Lewis said.

Though poverty, natural disaster and demand for cheap labour and prostitution also contributed to human trafficking in Sri Lanka, conflict could accelerate the problem.

"You will get dysfunctional families. You will get young men turning to crime," Lewis said.