North Korean leader Kim Jong-Un guided the military's latest rocket-firing drill, state media said Sunday, confirming the missile launch which was conducted in defiance of UN censure.

Saturday's launch was the first since the UN Security Council on July 17 officially condemned Pyongyang for its recent series of ballistic missile tests, in violation of UN resolutions.

The North's state news agency KCNA described the missile launch by the army as a "rocket-firing drill" to simulate a strike on military bases in South Korea where 28,500 US troops are stationed.

"(Kim) examined a firing plan mapped out in consideration of the present location of the US imperialist aggressor forces' bases... and under the simulated conditions of the battle to strike and destroy them before guiding the drill," it said.

The launch was intended to mark the July 27 anniversary of the ceasefire agreement at the end of the 1950-53 Korean War, KCNA said.

It did not say where the drill took place.

Seoul's army said earlier the North had fired a short-range missile into the sea Saturday night -- the latest in a recent series of launches that heightened tension on the peninsula.

The North often fires missiles and rockets as a show of force or to express anger at perceived provocations, but the frequency of the recent tests -- six in the past month -- is unusual.

"The North fired... a short-range ballistic missile into the East Sea (Sea of Japan) at 9:40 pm (12:40 GMT)," a spokesman for Seoul's defence ministry told AFP.

- Close to border -

The missile, with an estimated range of 500 kilometres (300 miles), was fired in the northeastern direction from Jangsan Cape in the North's western coast -- only 12 miles away from the tense sea border with the South, he said.

Pyongyang's recent missile launches were carried out at locations increasingly close to the border with the South -- a move analysts say is aimed at stepping up threats against Seoul.

The flashpoint maritime border on the Yellow Sea was a scene of several bloody naval clashes and the North's shelling of a border island in 2010 that left four South Koreans including two civilians dead.

Japanese Prime Minister Shinzo Abe said Tokyo had lodged a "strong protest" to the North against the latest launch.

"We need to let North Korea know that development of nuclear and missiles cannot go together with economic development," Abe told reporters during his trip to Mexico.

UN resolutions bar North Korea from conducting any launches using ballistic missile technology.

The UN's latest criticism on the North met with an angry response from the North, which called it "absolutely intolerable" and defended the missile launches as a response to "madcap war manoeuvres" by the US.

The launch came as Pyongyang has been playing hawk and dove in recent weeks, mixing its tests with peace gestures that have been largely dismissed by Seoul.

The two Koreas are currently trying to sort out logistics for the North's participation in the Asian Games, which begin in September in the South Korean city of Incheon.

"Our military sees the launch by North Korea, conducted while expressing its will to participate in the upcoming Incheon Asian Games, as part of its traditional dual strategy of engagement and pressure," Seoul's military spokesman said.