Prosecutors are planning to file an arrest warrant for Lee Sang-deuk, elder brother of President Lee Myung-bak and former six-term lawmaker, by the end of the week after he apparently admitted to several bribery charges during a Tuesday summons, a source said Wednesday.

The first-ever arrest of a sibling of an incumbent president is expected to lead to the probe expanding to officials ranging from the president’s right-hand man to opposition leaders, and into the possible slush fund created during the 2007 presidential election. Previously, sons of former presidents Kim Young-sam and Kim Dae-jung were arrested over irregularities during their tenures.

According to insiders at the special investigation unit at the Supreme Prosecutors’ Office, Lee Sang-deuk reportedly admitted to allegations that he received more than 500 million won ($441,000) from Lim Suk, chairman of Solomon Savings Bank, and Kim Chan-kyong, chairman of Mirae Mutual Savings Bank, in exchange for peddling his influence in evading a shutdown order.

Prosecutors are planning to file for the arrest so that they can delve into at least six other claims of irregularities by Lee.

The prosecutors suspect that many of the kickbacks given to Lee were used to help his younger brother win the presidential race in 2007. If convicted, Lee could spend up to five years behind bars, observers said.

The prosecutors are now zeroing in on a second target, Rep. Chung Doo-un of the ruling Saenuri Party, on suspicion of receiving more than 30 million won from Lim. Chung is scheduled to report himself to the prosecution on Thursday.

Chung is known to have introduced Lim to Lee in 2007. He allegedly received more than 30 million won from Lim through Lee Ho-young, an official in the Prime Minister’s Office. The money is also suspected to have been used to support Lee Myung-bak.

Chung said on his Twitter account that he had returned the money right after Lee Ho-young brought it to him. Chung, one of the president’s most trusted aides, said “accidents” took place in between the delivery of the money.

He said he was ready to face the prosecutors. “I will make sure that even dummies can understand what has happened,” he said.

Park Jie-won, floor leader of the main opposition Democratic United Party, on Wednesday repeatedly denied that he had received tens of millions of won from Lim as well as now-defunct Bohae Savings Bank management at a foreigner-only casino in Daegu.

“This is a political gambit against political leaders. The investigation should focus on digging on Lee Sang-deuk, Lee Myung-bak and their cronies,” he said.

By Bae Ji-sook (baejisook@heraldcorp.com)