North Korea launched two short-range missiles into the sea this week, the South Korean government reported on Thursday, as Seoul stepped up vigilance ahead of a visit by US Defense Secretary Ashton Carter.

The Kim regime on Tuesday fired two land-to-air projectiles into the Yellow Sea from Pyongwon county, on the western coast of North Korea, a spokesperson of Seoul’s defence ministry told Efe news agency.

He explained that the short-range missiles were of the KN-06 variety and travelled only a "few dozen kilometres" before falling into the sea.

He also said that the new missile launches "seems to be part of an annual military training exercise" and dismissed the possibility of their being related to Carter’s visit to Seoul.

Carter is scheduled to arrive in South Korea on Thursday for a three-day visit which includes a bilateral meeting on Friday with his South Korean counterpart Han Min-koo and other military authorities.

The US official is expected to discuss matters related to the military threat from North Korea, which has a potent arsenal of missiles and is developing nuclear weapons.

Authorities in Seoul have heightened vigilance of North Korean army movements ahead of Carter’s visit, according to the defence ministry.

The missile launches by Pyongyang, which has made other similar launches in recent weeks, and the US defense secretary’s visit come at a time of tension on the peninsula.

Joint US-South Korean military drills are underway on South Korean territory, and the Kim regime has responded with missile launches and threats.

The US has a permanent force of some 28,500 troops in South Korea to defend its ally against North Korean aggression, an arrangement dating back to the early 1950s and the end of hostilities in the Korean War.