North Korea has threatened to open fire on South Korea if anti-Pyongyang leaflets are dropped over its territory.
Defectors and human rights activists plan to send giant balloons containing 200,000 leaflets criticising North Korea's government over the country on Monday morning.
Inside the leaflets will be 1,000 \$1 notes - highly prized by the impoverished people of the north.
North Korea said if the leaflets were dropped, a "merciless military strike by the Western Front will be put into practice without warning", according to state news agency KCNA.
It said it would target a tourist area in the border city of Paju a few miles from the demilitarised zone that separates the two countries.
"The KPA (Korean People's Army) never makes any empty talk," KCNA quoted military commanders as saying.
In November 2010, North Korea fired about 170 rounds of artillery on Yeonpyeong Island and the surrounding waters near the Yellow Sea border, with some 90 shells landing on the island. And in 2010, the North was widely blamed for sinking a South Korean naval ship, although it denied responsibility.
The group planning the leafleting, Fighters for a Free North Korea, said they had no intention of calling it off.
"We had similar threats last year and they did not stop us before and this is not going to stop us this time," said Pak Sang-hak, a North Korean exile who defected to the South 12 years ago.
The threat came a day after South Korean President Lee Myung-Bak made a surprise visit to an island close to the disputed maritime border that was shelled.
There have been widespread concerns in the South that Pyongyang may try to instigate a military clash that would temporarily destabilise the Korean peninsula in the run up to the presidential election in December.
Kim Yong-Hyun, a professor at Dongguk University, said: "I think this is a bluff. I don't think they mean to actually target and shell the area.
"It could be an indirect reaction to what President Lee said (on Thursday) and the North is also seeking to drive wedges between conservatives and liberals ahead of the presidential poll," Kim said.
On Wednesday, South Korea announced an annual, large-scale military exercise aimed at countering threats from North Korea.
The week-long Hoguk exercise beginning on October 25 will involve 240,000 army, navy, air force and marine corps personnel, with 500 US soldiers also taking part.
Some 28,500 US military personnel are stationed in the South, a legacy of the Korean War that ended with a ceasefire but not a peace treaty, leaving the two Koreas still technically at war.