South Korea's government said Thursday it would not stop activists launching leaflets with news of Arab protests into North Korea, despite Pyongyang's threats to open fire in retaliation.

A defector group has said it will float leaflets and video footage across the heavily fortified border next week, possibly on Monday or Tuesday if the wind is in the right direction.

"There is nothing illegal about the activities," said Lee Jong-Joo, a spokeswoman for the South's unification ministry, which handles inter-Korean affairs.

Park Sang-Hak, leader of Seoul-based Fighters for Free North Korea, said the group would launch 200,000 leaflets plus DVDs and USB flash drives.

He said the DVDs and flash drives were targeted at schools, colleges and public institutions that may have computer access. Second-hand DVD players are also brought in from China and are reportedly not uncommon in some areas.

The disks and memory sticks would carry news of uprisings in Egypt and Libya and of a recent trip to Singapore by Kim Jong-Chol, second son of leader Kim Jong-Il, to attend an Eric Clapton concert.

The South's military has also reportedly recently sent leaflets with news of the Middle East revolts. Private groups have for years sent flyers attacking the North's regime.

Bundles of leaflets and other material are slung under huge helium-filled balloons, with timers set to open packages over the North's territory.

The North has always reacted angrily to such launches. But analysts say the Kim dynasty, which has ruled with an iron fist since 1948, is especially eager to exclude news of revolts against Arab despots.

Tensions are also high amid an ongoing US-South Korean military exercise that the North sees as a rehearsal for invasion.

On Sunday Pyongyang's military threatened to open fire on border areas such as Imjingak where balloons are launched.

"Our military in self-defence will launch direct, targeted firing attacks towards the origins of such anti-republic propaganda activities... if the practice continues despite our repeated warnings," it said.

"We're not afraid of the threat... North Koreans have every right to know what's going on in the outside world no matter how hysterically the regime reacts," Park told AFP, speaking of the planned launch at Imjingak.

"Many North Koreans know a lot about Libya so the news about what's going there will have some impact in the North," he said, adding that its leader Moamer Kadhafi is described as a "revolutionary comrade" of Kim Jong-Il.

Regarding the Clapton concert footage, Park said North Koreans were taught such entertainment was capitalist decadence. "They need to know what the leader's son is doing right now."

Seoul says it has no legal power to halt private leaflet launches.

It has sometimes urged activists to desist when the North threatened retaliation but "things have changed" since military provocations last year, said ministry spokeswoman Lee.

The North's deadly shelling of a frontier island last November killed four South Koreans including two civilians, and its alleged torpedo attack on a Seoul warship left 46 sailors dead in March 2010.

"Now with even the military, a part of our government, talking about psychological warfare against the North, we don't urge private activists to stop the practice," Lee said.

The two sides halted official cross-border propaganda under a 2004 deal, but the South partially revived it following the warship sinking.

The South's military has floated balloons into the North carrying news of Arab uprisings along with basic household goods that are in short supply in the impoverished nation, a lawmaker said last week.

A unification ministry official later confirmed the military launches.