The DPRK fired what appeared to be several land-to-ship missiles off its east coast on Thursday, South Korea's military said
The launches came a day after the South postponed full deployment of a controversial US anti-missile system designed to deter a North Korean attack.
The launches were the latest in a fast-paced series of missile tests defying world pressure on Pyongyang to rein in its weapons programme. They come than a week after the UN Security Council passed fresh sanctions on the North Asian state.
South Korea on Wednesday said it will hold off on installing the remaining components of the US Terminal High Altitude Area Defense (THAAD) system. The THAAD deployment angered North Korea's main ally, China.
Under third-generation leader Kim Jong-un, the DPRK has been conducting missile tests at an unprecedented pace in an effort to develop an intercontinental ballistic missile (ICBM) capable of hitting the mainland United States.
Compared to the different types of ballistic missiles Pyongyang has recently tested, the missiles launched on Thursday are considered to be more defensive in nature, designed to defend against threats such as enemy warships.
North Korea unveiled a number of new weapons at a massive military parade on April 15 to mark the birth anniversary of the state's founding leader Kim Il-sung and has since tested some of them.
"What appeared to be a new type of land-to-ship missile equipped with four launching canisters was unveiled at the parade," said Kim Dong-yub, a military expert at Kyungnam University's Far Eastern Studies in Seoul. "I think this might be what was used today."
THAAD defence delayed
Thursday's launch was the fourth missile test by North Korea since South Korean President Moon Jae-in took office on May 10 pledging to engage in dialogue with Pyongyang. Moon says sanctions and pressure alone have failed to resolve the growing threat from the North's advancing nuclear and missile programme.
Moon had also promised to review the deployment of the THAAD system in South Korea, a decision that was made by the government of his conservative predecessor, Park Geun-hye. On Wednesday, Moon's office said installation of four additional launchers would be halted until an assessment of the system's impact on the environment was completed.
Two launchers of the full six-launcher THAAD battery, as well as the system's far-reaching radar that China worries could upset the regional security balance, have already been installed at a deployment site in the southeastern city of Seongju. Those elements will stay in place, South Korea said.
China pressures South Korea
The introduction of the THAAD system has sparked protests in South Korea and a backlash in China against South Korean business interests.
The Global Times, published by China's official People's Daily, said in an editorial that no matter the outcome of the environmental study, South Korea's announcement could reduce friction.
"Obviously, the pressure China puts on South Korea has taken effect. Seoul's will has been shaken," the paper said. "However, attitude is not everything. Without solving the problem of THAAD, the pain it has brought to bilateral relations will not disappear, and South Korea must swallow some of the bitter results."
China should work with Russia on counter-measures to THAAD, the Global Times added.
There was no immediate official reaction from China to the latest missile test.
US President Donald Trump has been pressing China aggressively to rein in North Korea, warning that all options, including a pre-emptive military strike, are on the table if Pyongyang persists with its nuclear and missile development.
Seoul, Tokyo and Washington were analysing the launches for further information, officials said.
Japan's navy and air force conducted military drills with two US aircraft carriers in the Sea of Japan last week, following similar joint US-South Korea exercises.
"North Korea likely wanted to show off its ability to precisely target a large warship, in relation to the joint military drills involving US aircraft carriers," Roh Jae-cheon, South Korea's Joint Chiefs of Staff spokesman, told a media briefing.
"By testing different types of missiles, North Korea also appears to be aiming to secure the upper hand in relations with South Korea and the United States."
The isolated country, which has conducted dozens of missile tests and tested two nuclear bombs since the beginning of 2016 in defiance of UN Security Council resolutions, says the programme is necessary to counter US aggression.