Police on Tuesday called in North Korean defector brothers over their groups' anti-North Korea leafleting campaign, which Seoul views as a breach of law and Pyongyang vehemently criticizes.

Park Sang-hak, head of Fighters for a Free North Korea, and his younger brother Jung-oh, who leads another defector group, Kuensaem, showed up for questioning at the Seoul Metropolitan Police Agency at 9:20 a.m.

Police were trying to determine whether the brothers' campaign has breached the inter-Korea exchange and cooperation act.

The brothers are known to have scheduled their attendance in advance with authorities.

Defying the government's warning against leafleting, the older Park claimed that his group sent some 500,000 leaflets carried by 20 large helium balloons over to the North on Monday last week.

Cheong Wa Dae earlier warned that the government would crack down on such acts, which it said constitute a violation of laws including the inter-Korean exchange and cooperation act.

On June 10, the Unification Ministry filed a criminal complaint with police against the two organizations and decided to revoke their business permits.

The campaign to scatter leaflets that criticize the North Korean political system and the North's ruling Kim family has recently been a major source of confrontation between the two Koreas.

Police plan to question the brothers on various suspicions raised against their activist groups that have been leading the leafleting campaign.

Last week, police raided the offices of the two defector groups led by the brothers.

They have also been probing into the case by interviewing residents in the border towns of Gimpo, Paju and Yeoncheon in Gyeonggi Province and Gangwha in Incheon, west of Seoul.

Police are expected to decide whether to push for their indictment following the questioning. (Yonhap)