North Korea vowed Thursday to push ahead with further strategic guided-missile tests, defying international calls to curb its weapons programme as the Chinese president arrived in Seoul for a visit seen as a snub to Pyongyang.

"(North Korea) will continue to hold drills of launching high-precision tactical guided missiles," said a spokesman for the Korean People's Army (KPA) Strategic Force, calling the tests a "legitimate exercise" of sovereignty.

North Korea has conducted a series of missile tests in the past week -- seen by some a display of pique with Chinese President Xi Jinping's two-day state visit to Seoul.

China is North Korea's sole major ally, but while Xi has met four times with South Korean President Park Geun-Hye -- including two summits -- he has yet to sit down with North Korean leader Kim Jong-Un.

The United States criticised the recent missile launches as "problematic" and "destabilising", while Seoul and Tokyo also lodged protests.

The first in the series of tests last Thursday was hailed by the North's state media as that of a new "cutting-edge" guided missile which marked a "breakthrough" in the North's military capabilities.

The South said the second test on Sunday was of two short-range Scud missiles with a range of about 500 kilometres.

On Wednesday the North fired two rockets with a range of around 180 kilometres (110 miles).

The South said there were a number of possible motives for the multiple tests, ranging from a display for domestic consumption, to a show of strength for the international community or a warning to Seoul.