By Tomas Sarmiento and Miguel Gutierrez

MEXICO CITY (Reuters) - Mexico's Congress on Thursday approved a long-awaited law to crack down on money laundering in a bid to attack the finances of the country's powerful drug cartels.

The law, proposed two years ago by President Felipe Calderon as part of his offensive against drug gangs, was passed by the Senate on Thursday. The lower house passed it earlier this year.

The new federal law puts restrictions on cash purchases of real estate, jewelry, armored cars and other assets that criminals use to launder illicit funds. Companies will be required to report large cash purchases under the law.

"There is an outcry from society to weaken the financial structures of organized crime, and that is what this law is about," said Senator Roberto Gil, a member of Calderon's conservative National Action Party.

Nearly 60,000 people have been killed since Calderon launched a military-led assault against drug cartels after taking office in late 2006.

Dozens of drug lords have been killed or captured since then, but Calderon and the country's lawmakers have been criticized for not doing enough to attack cartel finances.

"We have to stem the flow of dirty money in Mexico, which has been the main driver of the growing violence in the country," said Senator Arturo Zamora from the Institutional Revolutionary Party (PRI).

President-elect Enrique Pena Nieto, who will return the PRI to power when he takes office in December, has said he will fine-tune the strategy to reduce violent crime linked to the drug war.

The bill now goes to Calderon's office for ratification, but is only set to take effect nine months later to give authorities time to prepare to enforce the law.

Zamora said estimates for the amount of illegal funds laundered in Mexico range from around $10 billion a year to as high as $45 billion.

(Writing by Gabriel Stargardter; Editing by Michael O'Boyle, Simon Gardner and Cynthia Osterman)