Local civic groups urged prosecutors on Sunday to toughen their probe into allegations that a former chairman of Shinhan Financial Group Co. bribed politicians to oust his then rival in the company in 2010.

The groups, including Solidarity for Financial Reform, say Ra Eung-chan, who headed the banking group from 2001 to 2010, provided 300 million won ($273,000) to then President Lee Myung-bak's brother through a middleman in 2008.

They believe Ra did this to purge the then CEO of the banking group, Shin Sang-hoon, in a high-profile internal strife over management control.

The scandal concluded with the resignations of Ra, Shin and another Shinhan executive in 2010.

On Friday, prosecutors summoned Ra for the first time since a complaint was filed by the groups in 2013 for questioning. Ra had refused to be interrogated, complaining of Alzheimer's disease.

"Ra appeared relatively healthy on Friday despite claiming to suffer from Alzheimer's," the groups said in a statement. "We can't help but ask why the prosecution took so long to call him in for questioning."

The groups vowed to ask the justice ministry for supervision in case prosecutors "continued to fail to investigate the case properly."

The groups also plan to file a separate complaint on Monday alleging that Ra and the then head of Shinhan Bank, the flagship unit of the banking group, illegally surveyed consumer data for an unidentified period. (Yonhap)