South Korean activists said Monday they planned to launch millions of anti-Pyongyang leaflets into North Korea, a move likely to escalate already elevated tensions on the divided peninsula.

Conservative activists, including many North Korean defectors, have been carrying out leafleting exercises using giant helium balloons for years -- a practice that infuriates Pyongyang which has threatened military strikes in response.

In October 2014, North Korean frontier guards attempted to shoot down a set of balloons, triggering a brief exchange of fire across the border.

Defector-turned-activist Park Sang-Hak said the planned launch would take place on March 26 at Imjingak, a park located in the border city of Paju.

"We will fly 10 million propaganda leaflets criticising Kim Jong-Un's severe violation of human rights," Park said in a statement.

The event is to coincide with Saturday's anniversary of the sinking of a South Korean warship in 2010, with the loss of 46 sailors. Seoul pinned the blame on the North and froze trade and investment ties.

The South Korean government says the activists have a right to carry out leaflet launches, although it has, in the past, used police to block such exercises during moments of heightened inter-Korean tension.

Tensions have escalated sharply in recent weeks, with North Korean leader Kim Jong-Un threatening further nuclear tests and missile launches, partly in response to ongoing South Korea-US military exercises.

The Unification Ministry said officials would have to consider whether a leaflet launch in the present atmosphere might trigger a North Korean response that would "threaten the lives and property of our citizens".

Following North Korea's fourth nuclear test on January 6, South Korea resumed blasting a mix of K-pop and propaganda messages into the North, using giant banks of speakers on the heavily militarised border.

North Korea has responded by dropping its own leaflets over the border, attacking South Korean President Park Geun-Hye.