The Convention against Corruption is designed to stamp out graft by requiring states to criminalise bribery, embezzlement, money laundering and abuse of power.

For the first time, it includes provisions that commit its signatories to returning assets stolen and lodged overseas to their country of origin.

But some campaigners fear it does not go far enough, since rules on political party funding and on private sector corruption are only optional.

'Real difference'

Still, UN officials said the treaty represents a step forward in fighting corruption, which many judge to be one of the main forces holding back developing economies.

The convention has teeth... I believe it's going to get a few fish Michael Costa, UN Office on Drugs and Crime executive director

"This treaty can make a real difference to the quality of life of millions of people around the world," said UN Secretary-General Kofi Annan in a message sent to the UN Office on Drugs and Crime (UNODC), which is responsible for the treaty.

The treaty will be formally adopted by the UN General Assembly next month, before a signing ceremony in Mexico in November.

Before it comes into force, 30 countries must ratify it as well as signing it, a process that could take as long as two years.

Getting the money back

The provision on stolen assets is the most important development for poorer countries, according to UNODC head Michael Costa.

"(The convention) has teeth... I believe it's going to get a few fish," he said.

"It is much more than just trying to stop this sort of activity, but trying to salvage economies which otherwise would go bankrupt."

The asset return provisions could help countries like Nigeria, which has striven for years to reclaim billions of dollars stolen by late dictator Sani Abacha, much of which remains in UK and Swiss bank accounts.

Earlier this week Nigerian officials told the Financial Times newspaper that they were giving up on seeking help from the UK government in retrieving the billion dollars or more alleged to be held in London banks.