SEOUL (AFP) - South Korean prosecutors raided the house and office of ex-president Lee Myung Bak's brother on Monday (Jan 22), reports said, probing allegations that the former head of state took bribes from the national spy agency during his term.

Lee Sang Deuk, 82, who was seen as highly influential during his younger brother's time in office, is suspected of receiving hundreds of millions of won from the National Intelligence Service (NIS), Yonhap news agency reported.

Investigators from the Seoul Central District Prosecutors' Office searched the elder brother's home and office and confiscated documents and computer hard drives, according to Yonhap.

Lee Sang Deuk, a former lawmaker, was found guilty of corruption in a separate case in 2013 and served 14 months in jail.

The raid comes as part of a widening probe into illicit transfers of funds between the presidential office and the spy agency during the administrations of Mr Lee Myung Bak and his ousted successor Park Geun Hye, both of them conservatives.

South Korea's current left-leaning President Moon Jae In has vowed to "fix past wrongs" in the country's governance, calling them "accumulated evils".

Mr Lee, who stepped down at the end of his single five-year term in 2013, denounced the probe as a "political revenge" last week after two of his closest aides were arrested for allegedly taking bribes from the NIS.

South Korea has a pattern of investigating its former leaders once their political opponents take office.

During Mr Lee's own term, former liberal president Roh Moo Hyun was questioned over alleged corruption and subsequently committed suicide.

Park, who was impeached last year, is currently on trial for corruption and abuse of power and prosecutors this month added two new charges - bribery and embezzlement - to her 18-count corruption indictment, accusing her of accepting 3.65 billion won (S$4.4 million) from the spy agency while she was in office.