North Korea on Wednesday defended a recent series of missile and rocket tests as justifiable self-defence drills and hit back at "vicious" criticism of them by Seoul and Washington.

The tests were largely seen as a calculated display of military muscle-flexing to reflect the North's anger over ongoing South Korea-US military exercises.

In a statement carried by the North's official KCNA news agency, a Korean People's Army (KPA) spokesman said the tests -- which violated UN sanctions banning any ballistic missile test by Pyongyang -- were "ordinary military practice".

The North fired half a dozen short-range missiles into the sea off its east coast over the past week, followed by a volley of rockets from multiple launchers on Tuesday.

South Korea called the launches a "reckless provocation" while Washington urged Pyongyang to halt the tests immediately, saying they risked inflaming regional tensions.

The KPA spokesman said all the missiles and rockets -- tested at ranges of between 55 kilometres (33 miles) and 500 kilometres -- had followed their planned trajectories "without the slightest error."

Stressing that the tests did not have the "slightest impact" on regional peace or stability, the spokesman hit back at US and South Korean criticism.

"The US and its followers that harbour hostility towards our republic... are viciously attacking us from the very moment our rockets soared towards the sky," he said.

The "real provocations", he added, were the joint military drills being held in South Korea that began on February 24.

North Korea routinely condemns the annual South-US exercises as rehearsals for invasion.

Despite tensions over the drills and the North's missile tests, cross-border ties are currently enjoying an upswing.

The two Koreas recently held the first reunion for more than three years of families divided by the Korean War -- an event that raised hopes of greater cross-border cooperation.

The KPA statement was released just hours after the South made a formal request for talks next week aimed at organising further reunions.

The army spokesman stressed that warmer relations would do nothing to erode the North's commitment not only to developing its ballistic missiles but also to its nuclear weapons programme.

"Our republic and people will not stop our legitimate rocket launches or stop developing our self-defensive nuclear deterrent because of the lure of improved ties," it said.

Addressing a parliamentary defence committee in Seoul on Wednesday, South Korean Defence Minister Kim Kwan-Jin said the North's tests were clearly meant to be provocative and Seoul had stepped up surveillance.

"I don't exclude the possibility of the North conducting additional long-range missile launches or a nuclear test," Kim said.

Kim's ministry also said the tests had been carried out without due diligence, resulting in a Chinese airliner with more than 200 passengers crossing the trajectory of one of the rockets fired on Tuesday.

China's foreign ministry spokesman Qin Gang called on all sides to exercise "calm and restraint" to avoid any further escalation of tensions.