SEOUL -- Ex-president Roh Moo-Hyun expressed shame at letting down the nation as he became South Korea's third former head of state to be summoned in a corruption probe.

"I feel ashamed before my fellow citizens," Roh said before heading by bus from his retirement home on the southeast coast to Seoul to face questioning by prosecutors.

"I am sorry to have disappointed you."

The 62-year-old bowed slightly after making the brief statement outside his home to hundreds of journalists.

Roh has been summoned as a suspect in a multi-million dollar graft probe but prosecutors have not yet decided whether to arrest him.

The case has sparked a media frenzy along with sharp criticism of Roh, who won office partly on an anti-corruption platform and served from 2003 to 2008.

He has publicly apologised for his family's involvement in the case but denied personal involvement.

Five former presidents including Roh have been tarnished by scandals involving either themselves or their families. Apart from Roh, Chun Doo-Hwan and Roh Tae-Woo personally faced a criminal probe.

Chun and Roh Tae-Woo were convicted in 1995 of receiving bribes and inciting mutiny. Both were sentenced to death but pardoned in 1997.

Roh "wanted to be the first son of a new era, not the youngest child of the old era. But there's no chance of that now," JoongAng Daily said in an editorial lamenting the scandals.

TV news helicopters broadcast Roh's journey by coach from his home at Bongha, 450 kilometres (279 miles) southeast of Seoul.

Roh, accompanied by his aides and lawyers, arrived at the Supreme Prosecutors' Office in Seoul around 1:15 pm (0415 GMT) for questioning. He declined to talk to dozens of reporters as he went inside.

"I'll talk to you later," he said in answer to shouted questions.