More than 100 United Nations' members are meeting in Mexico to sign a landmark convention against corruption.
Mexico's President Vicente Fox has vowed to fight corruption
The first legally-binding international agreement on the issue is aimed at making it easier to hunt down corrupt officials and to recover illicit funds.
Mexico and the United States were among the first to sign at the three-day UN forum in the southern city of Merida.
The terms of the treaty were agreed in October, but will only enter into force when it is ratified by 30 countries.
Forty-three countries had signed the accord by late Tuesday, the UN legal affairs director Hans Corell was quoted by French news agency AFP as saying.
The Convention against Corruption will require states to criminalise bribery, embezzlement, money laundering and abuse of power.
For the first time, it includes provisions that commit its signatories to return assets stolen and lodged overseas to their country of origin.
The BBC's Mexico correspondent Clare Marshall says the motivation behind the treaty is to encourage developing countries in particular to take action over corruption rather than accept it as an inevitable part of society.
The aim is to crack down across the world on secret bank accounts and money laundering, both major impediments to a country's development.
The convention will require public officials to declare details of any foreign bank accounts and funds will be monitored.
Mexico - which has seen billions of dollars embezzled by officials - was among the first to sign up to the pledge.
"The issue of corruption is a real scourge for our economies and development," said President Vicente Fox.
"Strengthening the fight against corruption is to strengthen our fight against poverty."
US Attorney General John Ashcroft, who signed on behalf of the US, said corruption is "a tax on the poor".
"It steals from the needy to enrich the wealthy," he added.
Anti-graft campaigners have given a cautious welcome to the treaty, saying it must be supervised closely to have any effect.
Some campaigners fear it does not go far enough, since rules on political party funding and on private sector corruption are only optional.
"The convention is a very complex instrument," said Eduardo Bohorquez of Transparency International. "It's not the point of arrival but of departure."
The treaty must now be ratified by 30 countries - a process that may take as long as two years.
Mr Bohorquez said local governments must do their utmost to ratify the treaty and "ensure it is respected".