By Tim Cocks

ABUJA (Reuters) - Nigerian police were searching for the 82-year-old mother of the country's finance minister on Monday after she was kidnapped from her home by unknown assailants.

Nigeria is one of the worst countries in the world for kidnapping, a business which makes millions of dollars a year for criminal gangs.

Abductions are most common in oil producing areas, especially Delta state in the southeast where Kamene Okonjo was seized late on Sunday morning.

President Goodluck Jonathan hired Okonjo's daughter as finance minister last year. Ngozi Okonjo-Iweala's drive to reform a corrupt and closed economy has made her popular with Western powers and many Nigerians hoping for change.

But the former World Bank director has also ruffled powerful vested interests along the way, especially fuel marketers benefiting from a corrupt state subsidy scheme.

Speaking on local independent TV station Channels TV, Delta state Governor Emmanuel Uduaghan said a rescue operation was under way.

"I have directed that within 24 hours the woman should be fished out," he said.

Okonjo is a professor and the wife of the traditional ruler of her home town, Ogwashi-Uku.

An official in Delta State said investigations had not yet revealed whether she was kidnapped to extract a ransom or for political motives, but that Okonjo was involved in local politics and that seizing her may be some kind of scare tactic.

"If they are pledging to rescue her within such a short time frame, that probably means they know something about where she is and how to find her," the official said.

Gangs responsible for kidnappings throughout the Niger Delta, home to Africa's largest oil industry, are usually after ransoms. The majority of people abducted are Nigerians, but foreign oil and construction workers have also been targets.

Local newspapers report kidnappings almost daily and the victims are often professionals or relatives of politicians, although rarely anyone as high profile as Okonjo.

(Editing by Tom Pfeiffer)