"Thursday's missile tests were apparently made as part of a military drill but today's launches, which came on the eve of the US Independence Day, are believed to be aimed at political purposes," the official said.

Japan condemned the latest missile launches as a "serious act of provocation." "It is a serious act of provocation against the security of neighbouring countries, including our country," Chief Cabinet Secretary Takeo Kawamura was quoted by Jiji Press as saying. The Japanese government's top spokesman said the act was also against a UN Security Council resolution, according to Jiji.

Analysts said the North was flexing its military muscle amid tough international sanctions imposed on Pyongyang over its nuclear weapons and missile programmes.

Baek Seung-Joo of the Korea Institute for Defence Analyses said the North test-fires missiles three to four times each year to improve technology and maintain missile exports.

"Today's launches were part of a usual military drill but by firing 500km-range Scuds, the North was clearly displaying its ability to strike back against any international sanctions involving military means," informed Baek.