The unification ministry will inspect dozens of government-registered activist group later this month to look into whether they have been involved in sending anti-North Korea leaflets, a ministry official said Thursday.

The move comes as the ministry has been pushing to revoke the operation permits of two North Korean defector groups for sending leaflets to the communist state in defiance of the government's calls against such activity.

"It is part of efforts to strengthen supervision on their operation," the official told reporters on condition of anonymity.

"The probe will be conducted first on 25 entities, including 13 groups run by North Korean defectors, from late this month ... It will be expanded to others going forward."

He said that the probe will be carried out as some of the activist groups have been involved in sending anti-North Korea leaflets across the border, jeopardizing residents in border areas and heightening cross-border tensions, though he noted that it is one of many areas that will be looked into.

The sending of leaflets across the border by activist groups has emerged as a major source of cross-border tensions since Pyongyang called it a violation of an inter-Korean summit agreement and threatened to take a series of retaliatory steps against South Korea if it did not stop such activity.

North Korea also called South Korea an "enemy" and blew up a joint liaison office in its border town of Kaesong in anger over the leafleting issue last month.

The ministry has pledged to crack down on leafleting, filed a criminal complaint against two defectors groups and taken steps to revoke their operation permits. The ministry earlier said that the revocation decision could be finalized as early as this week.

Losing operation permits would make it hard for the groups to raise money for their activities, as revocation would make them ineligible for various benefits available to registered organizations. (Yonhap)