Poorer nations need more support to retrieve billions of dollars of stolen assets spirited away to global financial havens, officials at a United Nations anti-corruption conference in Bali said on Tuesday.

The task had been made tougher by the growing complexity of the world's financial system and the emergence of new financial centres prepared to take shady funds, they said.

"This difficulty has been compounded by systems of high technology, where people can conduct banking through hot messaging systems, through their mobile phones or through the Internet," Indonesian Foreign Minister Hassan Wirajuda told a ministerial discussion on asset recovery on the sidelines of the conference, which is being attended by more than 100 countries.

Accordingly, the track record of finding assets is patchy. It took the Philippines almost 18 years to retrieve some assets from the estate of the late Ferdinand Marcos. The former president amassed up to $10 billion (5 billion pounds) of stolen assets, a report by Transparency International estimates.

In the case of Nigeria's Sani Abacha, estimated to have taken up to $5 billion, it took five to six years to get at any money.

Indonesia has made little progress tracking down the fortune of the late former President Suharto, put by Transparency International at $15-$35 billion.

Last September, the World Bank and the U.N. launched the Stolen Asset Recovery Initiative, which aims to help poorer nations with technical assistance to retrieve assets.

"Time is of the essence" when trying to find the money, said Antonio Maria Costa, executive director of the U.N. Office on Drugs and Crime, which oversees a graft convention.

CRIMINAL OFFENCE

The United Nations Convention against Corruption, ratified by 107 nations, came into force three years ago and requires members to make corruption a criminal offence, as well as binding them to cooperate with each other over graft and to return stolen assets.

"Stolen assets rot quickly in idle bank accounts, rusty yachts, decaying real estate and devalued securities," Costa said in an earlier speech at the opening of the conference.

Huguette Labelle, chairwoman of Transparency International, said in an interview on Monday she was worried about the failure of some global financial centres - such as Liechtenstein, Singapore and Switzerland - to ratify the anti-graft convention.

Anton Thalmann, Swiss deputy state secretary, said his nation had returned $1.6 billion over 20 years to nations of origin and that "Swiss banking secrecy laws do not protect crooks".

"If you want to have an efficient sustainable financial centre you have to keep it clean," said Thalmann, adding separately to Reuters that Switzerland was expected to sign up soon to the convention.

Bribes received by public officials from less developed countries are put at $20 billion to $40 billion per year, or between 20 to 40 percent of official development assistance.

Robert Klitgaard, a corruption expert at Claremont Graduate University in Los Angeles, told a lecture at the conference that it was key to make an example of some high-profile corruptors.

"If a few big fish are fried and they see that" it sends a powerful signal, he said.