North Korea has deployed new rocket launchers along its border capable of hitting targets beyond Seoul, a report said Sunday.

Artillery units from the North were spotted replacing older multiple rocket stations with an upgraded version of the 240mm guns, Yonhap news agency said.

The agency quoted an unnamed government official as saying the new multiple rocket launchers with a maximum range of 70 kilometres (42 miles) could extend their reach beyond the South Korean capital.

The South's defence ministry declined to confirm the report.

North Korea has 5,100 multiple rocket launchers, according to military data.

It has been eager to upgrade its mainstream multiple rocket launchers, which pose a serious security threat to South Korea.

Residents in Seoul and neighbouring satellite cities, together home to nearly half the South's 49 million people, have always lived under threat of attack from the North's rockets and long-range artillery.

In 2010, North Korea using multiple rocket launchers shelled a South Korean island near the disputed Yellow Sea border, killing four people.