The North fired a short-range missile into the Sea of Japan (East Sea) overnight, it quoted a Seoul government source as saying.

'Intelligence authorities are now closely monitoring the situation,' the source said.

The communist state fired three short-range ground-to-air missiles from locations near its east coast on Monday, the same day it conducted an underground nuclear test that shocked the world.

It launched two more off its east coast on Tuesday, Yonhap news agency reported. South Korea's military says it does not comment on intelligence matters.

The missiles fired on Monday and Tuesday were said to have a range of 130 kilometres.

Several times in recent years, the North has test-fired short-range missiles in either the Yellow Sea or the Sea of Japan. The exercises are often staged to coincide with periods of regional tension. -- AFP