Seoul (AFP) – North Korea on Monday fired multiple ballistic missiles off its east coast, Seoul's military said, after weeks of mounting friction over a landmine explosion along their heavily fortified border.

Since the blast that injured three South Korean soldiers in the Seoul-controlled area of the Demilitarised Zone (DMZ), both countries have touted the test-firing of upgraded missile technology.

"Our military detected around 09:20 (0020 GMT) several ballistic missiles launched from the Pyongyang area towards the East Sea," the Joint Chiefs of Staff (JCS) said Monday, referring to the body of water also known as the Sea of Japan.

"Our military has stepped up surveillance and vigilance against possible additional launches," it added in its statement.

Japan's defence ministry separately confirmed the launch of at least one suspected ballistic missile.

Some of the North Korean missiles detected flew more than 900 kilometres (560 miles), the JCS said, while Seoul and longtime ally the United States were now conducting an analysis of their exact specifications.

South Korea's National Security Office convened an emergency security meeting following the launch to review the country's military readiness.

A joint Seoul-UN investigation last week concluded that North Korea had planted the landmines that exploded in the DMZ over a year ago, something Pyongyang has angrily denied.

Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, has blasted South Korean demands for an apology as "despicable" while separately rejecting an offer of medical equipment from Seoul.

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