South Korea's military said the communist North on Tuesday carried out its third launch of a short-range conventionally armed missile in less than a month.

"It's not a political or diplomatic act," Hill, the US envoy on North Korea, said in Tokyo when asked about the latest test.

"The North Korean army has these tests from time to time. It's a schedule based on their military training and testing program. It's not really a political act in this case," he said, while adding he knew of the test through media reports.

The missile test came just before UN inspectors were prepared to head to North Korea to verify that the communist state had shut down a reactor in line with a long-delayed US-backed agreement.

The US and other regional countries had also played down the earlier tests. North Korea agreed under international agreements not to launch longer-range ballistic missiles, but not short-range missiles.