North Korea fired multiple short-range ballistic missiles on Monday in what analysts said was a calculated move to grab attention as US Secretary of State Antony Blinken visits South Korea for talks.

Blinken is attending the third Summit for Democracy and met President Yoon Suk Yeol in Seoul early Monday. He is also meeting his South Korean counterpart on the sidelines of the event, for discussions now likely to be dominated by the allies' efforts to counter threats from the nuclear-armed North.

Washington and Seoul wrapped up one of their major annual joint military training exercises last week, prompting angry retorts and live-fire drills from nuclear-armed Pyongyang, which condemns all such exercises as rehearsals for invasion.

Seoul's military said it had detected the launch of "multiple short-range ballistic missiles" early Monday, which flew around 300 kilometres (186 miles) before coming down into the East Sea, also known as the Sea of Japan.

"We are closely sharing relevant information with the US and Japan and are maintaining utmost readiness," the Joint Chiefs of Staff added.

After meeting Yoon, Blinken "condemned the... launch of ballistic missiles by the DPRK and reaffirmed the United States' ironclad commitment to the ROK's security," Spokesperson Matthew Miller said, referring to North and South Korea by their official names.

Japan's top government spokesman Yoshimasa Hayashi said the North had fired three short-range ballistic missiles, which landed outside of the country's EEZ and did not cause any damage.

The launches come just days after Seoul and Washington's annual Freedom Shield drills, which this year involved double the number of troops, ended Thursday.

Pyongyang this month warned that Seoul and Washington would pay a "dear price" over the drills, and later announced that North Korean leader Kim Jong Un had guided an artillery unit it says was capable of striking the South Korean capital.

"It's a highly calculated move timing-wise by Pyongyang to fire multiple missiles to show they are capable of doing such an act even when the top US diplomat is in town," Professor Choi Gi-il of military studies at Sangji University told AFP.

North Korea typically stages missile launches "as a tit-for-tat" after US-South Korea joint drills, Han Kwon-hee of Korea Association of Defence Industry Studies told AFP.

Blinken's presence only adds to their motivation, he said, as it "means more attention from Washington and adds pressure on host Seoul."

- Boosting deterrence -


Monday's ballistic missile test is the North's second this year, after Pyongyang launched one tipped with a manoeuvrable hypersonic warhead on January 14.

Blinken landed in South Korea on Sunday afternoon ahead of the democracy summit, which runs from March 18 to 20 and will bring together government officials, NGOs and civil society members.

Seoul is one of Washington's key regional allies, and the United States has stationed about 27,000 American soldiers in the South to help protect it against the nuclear-armed North.

Conservative President Yoon has boosted ties with Washington and sought to bury the historical hatchet with former colonial power Japan to better guard against Pyongyang's threats.

So far this year, Pyongyang has declared South Korea its "principal enemy", jettisoned agencies dedicated to reunification and outreach, and threatened war over "even 0.001 mm" of territorial infringement.

"While South Korea conducted defence training last week alongside international partners, Kim Jong-un personally supervised several military exercises, and now while Seoul hosts a summit of democracies, North Korea fires more missiles," said Leif-Eric Easley, a professor at Ewha University in Seoul.

"The Kim regime's one-upmanship aims to show strength to its domestic audience, suggest costs on the Korean Peninsula for Seoul's international security cooperation, and warn Washington against increasing pressure on Pyongyang."

Blinken also met South Korean Foreign Minister Cho Tae-yul for discussions on boosting the alliance, as Washington and Seoul look to improve their so-called "extended deterrence" against North Korea.

After Seoul, Blinken heads to the Philippines.