Choi See-joong, a former top communications regulator with close ties to President Lee Myung-bak, appeared before prosecutors Wednesday to face questioning over allegations he took bribes in exchange for influence-peddling in a construction project.

The 75-year-old Choi on Monday admitted to accepting the money, not as payment for favors but to cover the cost of conducting opinion polls during Lee's election campaign in 2007. Choi played a key role in Lee's election victory at the time.

Responding to reporters' questions after arriving at the Supreme Public Prosecutors' Office, Choi curtly said, "I will faithfully undergo the investigation."

The prosecution was expected to seek a warrant to arrest Choi, after questioning him.

The revelation has dealt another blow to the Lee administration, whose image has been tarnished by a string of corruption scandals involving the president's aides and recently renewed allegations it conducted illegal surveillance on civilians in the past.

Opposition political parties have stepped up their offensive against Lee, demanding the presidential office promptly reveal the truth behind the allegations, and calling on the prosecution to open an investigation into his past campaign funds.

Moon Sung-keun, the acting chairman of the main opposition Democratic United Party, told a meeting of senior party officials the prosecution should "investigate in detail where the money came from and where it went, and all aspects of the 2007 presidential election funds."

Choi stepped down as chairman of the state-run Korea Communications Commission in January over a separate graft scandal involving one of his aides. He is now suspected of accepting between 500 million won ($439,000) and 600 million won in 2007-2008 from a former head of a property developer called Pi City, and helping the company win a permit to build a large trade complex in southern Seoul.

Prosecutors arrested a broker on Saturday on suspicion of delivering the money and imposed an overseas travel ban on Choi the following day. The Pi City developer had allegedly offered 1.1 billion won to the broker for delivery to Choi.

Prosecutors said they were also investigating the developer's claims that he gave large amounts of lobbying money to the same broker for delivery to former Vice Economic Minister Park Young-june, another close aide of Lee.

Investigators raided Park's home in Yongsan, central Seoul, and his office in the southeastern city of Daegu earlier in the day to secure further evidence, prosecutors said.

The former vice minister was recently embroiled in a stock manipulation scandal related to a diamond mining project in Cameroon. (Yonhap)