North Korea has fired several short-range projectiles from its east coast, South Korea's military says, as analysts argue the country is stepping up pressure against the US after February's failed Hanoi nuclear summit.
The South Korean military initially described it as a missile launch, but subsequently gave a more vague description.
If the unidentified projectiles were missiles, it would be the first missile launch since the North fired an intercontinental ballistic missile in November 2017.
Soon after that missile test, the North declared its nuclear force was complete, after which Pyongyang extended an international olive branch.
North Korean leader Kim Jong-un. Source: AAP
In Saturday's statement, South Korea's Office of the Joint Chiefs of Staff said the North fired several unidentified short-range projectiles from the east coast city of Wonsan around 9am, which flew from 70km to 200km.
The South Korean military said it was conducting joint analysis with the US, but experts said the projectiles seemed to be multiple rocket launchers.
Analysts said that no matter what type of projectile was fired, the timing of North Korea's latest action sent a message after the failed summit between leader Kim Jong-un and US President Donald Trump, where the two disagreed over dismantlement and sanctions relief.
North Korea Deputy Foreign Minister Choe Son-hui talks during a press conference. Source: AAP
"It is an expression of the North's frustration over stalled talks with the United States. It is a message that it could return to the previous confrontational mode if there is no breakthrough in the stalemate," Yang Uk, a senior research fellow at the Korea Defence and Security Forum, said.
White House Press Secretary Sarah Sanders said: "We are aware of North Korea's actions tonight. We will continue to monitor as necessary."
In Seoul, South Korea's presidential office said the country's defence minister, intelligence chief and security advisors were monitoring the situation.
US Secretary of State Mike Pompeo and South Korean Foreign Minister Kang Kyung-wha agreed to "cautiously respond" to the latest firing and to continue communications during a phone call on Saturday.
Japan's defence ministry said the missiles didn't reach anywhere near the country's coast, and there was no security threat.
During a summit with Russian President Vladimir Putin in late April, North Korea's Kim said peace and security on the Korean peninsula depended on the US, warning a state of hostility could easily return.
"The North wanted to deliver a message on security guarantees to Washington through the mouth of Putin, but the summit fell short of driving change in the US attitude, leading the North to take stronger action today," Hong Min, a senior researcher of Korea Institute for National Unification, said.
Trump raised the issue of North Korea during discussions with Putin on Friday, purportedly telling him "the need and importance of Russia stepping up and continuing to put pressure on North Korea to denuclearise."
Kim vowed in April to cease testing nuclear weapons or ICBMs, but the North has conducted other weapons tests.
