North Korea on Monday floated hundreds of propaganda leaflets into South Korea threatening the "annihilation" of the 6th Marine Brigade on Baeknyeong Island, the Joint Chiefs of Staff said.

The burst of belligerence comes less than a week after the execution of North Korean leader Kim Jong-un’s uncle Jang Song-taek, who was seen as a moderate.

The previous day, the North Korean propaganda website, Uriminzokkiri also threatened to "mercilessly throw a battering ram" at the South Korean government, calling its response to the execution of Jang a "political provocation."

Hundreds of the leaflets were found around the island on Monday morning, according to the JCS.

The North called the 6th Marine Brigade the "first target to annihilate," adding, "Means of strike with unprecedented destructive power have already set their sights on the target and are ready to fire."

Another leaflet said, "Baeknyeong Island will turn into a huge tomb." Some leaflets featured a picture of a burned skull and bones.

But a military spokesman said "no special movements” of North Korean forces have been detected either on the coast close to South Korea’s northwesternmost islands or anywhere else.

“We've been keeping watch on those areas as the North has consistently augmented troops and equipment there over the past years,” the spokesman added.

Since the shelling of Yeonpyeong Island in November 2010, the North has kept reinforcing troops and equipment along the west coast. Early this year, it deployed new 240 mm multiple rocket launchers with a range of 65-70 km and augmented 122 mm rocket launchers with a range of 20 km that fired shells at Yeonpyeong Island and moved them forward.

The South Korean military has also increased the number of K-9 self-propelled guns on those islands and deployed "Guryong" multiple launch rocket system and Spike missiles.