SEOUL - Lee Myung-bak, former president of the Republic of Korea, returned home on Thursday after a marathon interrogation by prosecutors over corruption, the last of the country's living ex-leaders to be embroiled in a criminal inquiry.

Allegations of graft involving his relatives and aides during his term have mounted in recent weeks as prosecutors investigate multiple cases of bribery amounting to millions of dollars.

The probe means that the country's all four living former presidents have been convicted, charged, or investigated for criminal offenses.

Lee spent more than 21 hours at the prosecutors' office in Seoul from Wednesday morning, and did not reply to questions from journalists outside as he left.

"President Lee denied most of the charges," a prosecutor was quoted as telling Yonhap news agency.

Lee, who was head of state from 2008 to 2013, has previously denounced the inquiry as "political revenge" and said on Wednesday he hoped it would be the "last time in history" that a ROK ex-leader was summoned for questioning by prosecutors.

"As a former president, I have a lot to say about this but I will spare my words," he told reporters when he arrived for the interrogation.

Prosecutors are thought likely to ask a court for an arrest warrant for Lee in the coming days.

But almost one in six ROK citizens - 15.3 percent - think he should be treated leniently because of his status as a former president, an opinion poll by Realmeter showed.

The figure rose to 50 percent among supporters of the main opposition Liberty Korea party - which Lee led under a previous name - with only 38 percent believing he should be strictly punished according to the law.

Among the population as a whole, 79.5 percent said he should receive no preferential treatment.

The allegations against Lee include claims that the Samsung Group bought a presidential pardon in 2009 for its chairman Lee Kun-hee, who had been convicted of tax evasion and given a suspended jail sentence.

Both Samsung and Lee have described the allegations as groundless.

Agence France-presse