South Korean President Lee Myung-Bak apologised on Friday after a seven-year-old girl was kidnapped overnight from her home and raped, sparking a public outcry.

Police have detained a 25-year-old man after the girl was snatched in the southwestern city of Naju while she was sleeping. She was raped and later found naked on a riverside road.

"On behalf of the government, I apologise to the people," Lee said during an unscheduled visit to national police headquarters.

It was the latest in a series of sexual assaults on women and children that have prompted calls for tougher punishment for offenders.

Last week, a convicted sex offender stabbed a man to death and badly wounded four other people in a drunken pre-dawn rampage in the southern city of Suwon.

The man, who was wearing an electronic tracking device, was accused of trying to rape and then stabbing a woman at a bar.

In 2009, a 57-year-old man was sentenced to 12 years in prison for beating and raping an eight-year-old girl after kidnapping her on her way to school.

She suffered permanent injuries, leading parliament to enact a law allowing information on convicted child sex offenders to be posted on a website.