North Korea threatened Wednesday to "deal merciless sledgehammer blows" to South Korea for allegedly disseminating leaflets critical of the communist regime amid fresh tensions over Pyongyang's missile launches.

The Committee for the Peaceful Reunification of Korea accused South Korea's military of scattering anti-Pyongyang leaflets and staging drills near their tense western sea border -- the scene of bloody skirmishes between the rival Koreas in recent years.

The allegation came about an hour before North Korea test-fired two medium-range ballistic missiles into the sea off its eastern coast in the wee hours of Wednesday, the latest in a series of saber-rattling moves against Seoul and Washington.

South Korea and the United States condemned the missile launches as a violation of U.N. Security Council resolutions that ban all ballistic missile tests by the communist state.

The latest missile launches were apparently timed with a summit among leaders of South Korea, the United States and Japan in the Netherlands. The three leaders stressed the importance of trilateral unity in dealing with North Korea.

The North has launched a barrage of short-range missiles and rockets into waters off its east coast in recent weeks, behavior that Seoul and Washington say is provocation.

The North's committee handling inter-Korean affairs also warned that inter-Korean relations would not improve as long as South Korea's military is allowed to hurt the dignity of North Korean leader Kim Jong-un.

"Our army and people will never pardon even the slightest act of hurting the dignity of the supreme leadership ... but deal merciless sledgehammer blows to its perpetrators," the committee said in comments carried by the North's official Korean Central News Agency.

The North's latest threat came a month after South and North Korea agreed to halt slander against each other during their first high-level talks in seven years.

South Korea's defense ministry quickly dismissed the North's allegation as groundless.

"The North's allegation is not true," defense ministry spokesman Kim Min-seok said, noting that South Korean activists sent leaflets from Baengnyeong Island, a South Korean border island near the sea border, on Monday.

Kim said the government has not floated leaflets since 2004 when the two Koreas agreed to halt propaganda warfare along their heavily fortified border.

For years, North Korean defectors in the South and conservative activists have flown anti-Pyongyang leaflets from near the heavily fortified border to help encourage North Koreans to eventually rise up against the Pyongyang regime.

The North has bristled at any outside criticism of its leader and has made several military threats against the South over the leaflets in recent years. The North has also repeatedly pressed South Korea to stop its activists from sending the leaflets.

South Korea has said there are no legal grounds to prevent activists from floating the leaflets, citing freedom of expression. (Yonhap)