The North test-fired five KN-02 missiles with a range of 120 kilometres (75 miles) from mobile launchers off its east coast on October 12.

Radio Free Asia, quoting an intelligence source, said four of the five missed the mark and one did not even launch properly.

“Two fell into the sea right after launch, another two missed the targets and the last one failed to launch,” the source said, according to a Korean-language report on the US-funded radio’s website.

South Korea’s military and National Intelligence Service would not comment. Yonhap news agency earlier this month quoted a source as saying three of the five missiles “may have fizzled”.

The launches were the first reported since early July, and came amid international efforts to bring the hardline communist state back to six-nation nuclear disarmament talks.

South Korea and the United State denounced the launches as violating UN Security Council resolutions banning ballistic missile activities by the North.

In addition to launching long-range and medium-range missiles, the North has often launched short-range projectiles off its coasts in recent years.

Seoul officials have said the short-range tests are largely aimed at improving accuracy and performance, although the launches are also sometimes timed to make a political point.

The KN-02 missile is a modified version of the Soviet-designed SS-21 missile.