North Korea fires 'unidentified ballistic missile' towards sea

North Korea has fired a ballistic missile, Seoul's military said Wednesday, days after Pyongyang threatened to down US spy planes that violated its airspace.

"North Korea fired an unidentified ballistic missile towards the East Sea," the Joint Chiefs of Staff said, referring to the body of water also known as the Sea of Japan.

Relations between the two Koreas are at one of their lowest points ever, with diplomacy stalled and North Korean leader Kim Jong Un proclaiming his nation an "irreversible" nuclear state and calling for increased weapons development, including tactical nukes.

In response, Seoul and Washington have vowed Pyongyang would face a nuclear response and the "end" of the current government in North Korea were it to ever use its nukes against the allies.

On Monday, North Korea accused a US spy aircraft of violating its airspace and condemned Washington's plans to deploy a nuclear missile submarine near the Korean peninsula.

A spokesperson for the North's Ministry of National Defence said the United States had "intensified espionage activities beyond the wartime level", citing "provocative" flights made by US spy aircraft over eight straight days this month and one reconnaissance plane that intruded into its airspace over the East Sea "several times".

"There is no guarantee that such a shocking accident as the downing of the US Air Force strategic reconnaissance plane will not happen in the East Sea of Korea," the spokesperson said in a statement carried by the official Korean Central News Agency.

North Korean leader Kim Jong Un's powerful sister Kim Yo Jong said that a US spy aircraft had violated the country's eastern airspace twice on Monday morning, according to a separate statement.

Kim Yo Jong said the North would not respond directly to US reconnaissance activities outside of the country's exclusive economic zone, but warned it would take "decisive action" if the US military crossed its maritime military demarcation line.

Washington said in April that one of its nuclear-armed ballistic submarines would visit a South Korean port for the first time in decades, without specifying an exact date.

North Korea has conducted multiple sanctions-defying launches this year, including test-firing its most powerful intercontinental ballistic missile and attempting to put a military spy satellite into orbit in May.

South Korean President Yoon Suk Yeol has ramped up defence cooperation with Washington in response, staging joint military exercises with advanced stealth jets and powerful US strategic assets.

Yoon is set to attend a NATO summit in Lithuania this week, seeking stronger cooperation with the alliance's members over North Korea's growing nuclear and missile threats, his office said.

South Korea and the United States are set to start their major annual joint military exercises, known as Ulchi Freedom Shield, next month.

North Korea regards all such exercises as rehearsals for invasion and has described them as "frantic" drills "simulating an all-out war against" Pyongyang.

/KN/