Twenty students were found to have fallen victim to child abuse, a pangovernmental investigation into thousands of students who missed classes for more than seven days without prior notice on Friday.

Four cases have already been sent to the prosecution, and investigations are being underway for the other 16 cases, the officials said.

They were among a total of 6,871 cases of students who did not attend school for more than seven days in March, according to the Ministry of Education, which conducted a joint investigation into the matter with the Ministry of Health and Welfare and the Korean National Police Agency. High school students were not included in the investigation.

All of these students missed classes without excuses of absence, such as family celebrations or sick leave, according to the authorities.

No signs of violence, abuse or other criminal acts were found outside of those 20 casess, according to the government.

The probe kicked off after parents in Incheon were arrested in February this year for beating their son to death. The child was reported absent from elementary school before the death was discovered.

"There are growing concerns that children's longtime absence from class might be an omen for educational negligence or child abuse. (The government) will continue to detect children vulnerable to domestic violence to prevent any further child deaths," Education Minister Lee Ju-ho said in a ministerial-level meeting Friday.

The ministry said it provided psychological counseling and learning support activities to the 20 abused children. Those services were provided to other vulnerable students, such as lone parents, the disabled and impoverished households, too.

"To protect students from child abuse, the ministry will conduct checks twice a year on every student absent from school for more than seven days," the ministry said.