The unification ministry reaffirmed its vow Friday to stop North Korean defectors from sending anti-Pyongyang leaflets and other materials to the communist state, amid a spike in cross-border tensions caused by the North's shocking demolition of a joint liaison office.

The government has sought to stop the leafleting on the grounds that it could further aggravate inter-Korean tensions and undermine the safety of residents near the border.

North Korea has lashed out at South Korea for failing to prevent leafleting. It recently blew up a liaison office in its border town of Kaesong, threatening more retaliatory steps going forward.

"In close cooperation with the police and local authorities, the government will beef up its crackdown, including the response on the ground," Cho Hey-sil, the ministry's deputy spokesperson, told a regular press briefing.

"We will push ahead to strictly prevent the act of sending leaflets and other materials into North Korea," she said.

Keunsaem, a civic group led by North Korean defectors, said that it has temporarily suspended a plan to float plastic bottles containing rice into the North in the face of heightened cross-border tensions.

Another defector group, Fighters for Free North Korea, however, plans to send about 1 million leaflets across the border next Thursday to commemorate the 70th anniversary of the Korean War.

Last week, the unification ministry filed a criminal complaint against the two defector groups with regard to the leafleting issue. Police officers have been stationed to border areas to block any such activity and prevent a possible clash between activists and residents.

Defector groups and other activists have occasionally sent plastic bottles of rice or leaflets via giant balloons sharply criticizing the North Korean regime and its leader. (Yonhap)