By Tamara Walid

DOHA (Reuters) - Corruption costs developing nations $20 to $40 billion each year, while emerging markets and financial centers are increasingly havens for stolen assets, a top World Bank official said Saturday.

Managing director Ngozi Okonjo-Iweala said "concerted global action" by both developed and developing states was needed to stem the flow of illicit funds and urged governments to ratify the United Nations Convention Against Corruption (UNCAC).

"There's an estimate that $20-$40 billion a year, in terms of corruptly stolen assets, leaves developing countries to go to developed countries each year," Okonjo-Iweala, a former Nigerian finance minister, told Reuters ahead of an anti-corruption conference in the Qatari capital.

"Now increasingly, we find that emerging market countries (and) financial centers are also harbors for this money."

The World Bank official said the pledge by the Group of 20 nations (G20), meeting this weekend in Scotland, to help prevent illicit outflows of capital and seek the return of stolen assets to developing countries, was a welcome first step.

"Now what we need to do is move to action," she said. "Developed countries that have these assets have to implement the UNCAC convention and send these assets back, and developing countries need to make the move to request the assistance from developed countries."

Adopting the UN convention would provide a framework to fight corruption, she said, and help overcome thorny legal hurdles in different jurisdictions.

"So if countries really want to do it, they can because they can waive all those legal requirements, freeze the assets, seize them and send them back," she said.

Okonjo-Iweala said she hoped the UN anti-corruption convention "will not be a nice plan that would gather dust" but one every country needed to sign on to.

"When you ratify, you have to domesticate it within your own legal environment," she said. Continued...