The United States, Japan and South Korea on Sunday vowed a "strong and resolute response" if Pyongyang carried out a nuclear test.

A record-breaking recent spate of missile tests by North Korea has sent fears soaring that such a test -- its seventh -- may happen soon.

US President Joe Biden held talks on the crisis with allies Japan and South Korea in Phnom Penh Sunday, on the eve of a crunch meeting with Chinese counterpart Xi Jinping, whom he will press to rein in North Korean leader Kim Jong Un.

Biden, Japanese Prime Minister Fumio Kishida and South Korean President Yoon Suk-yeol issued a joint statement condemning the recent barrage, which included an intercontinental ballistic missile.

"They reaffirm that a DPRK nuclear test would be met with a strong and resolute response from the international community," the statement said, using an abbreviation for North Korea's official name.

The trio met on the sidelines of an East Asian summit in the Cambodian capital.

"President Biden reiterated that the US commitment to defend Japan and the ROK is ironclad and backed by the full range of capabilities, including nuclear," the statement added, using an abbreviation for South Korea's official name.

Pyongyang ramped up missile launches in response to large-scale US-South Korean air exercises, which it described as "aggressive and provocative".

Experts say Pyongyang is particularly sensitive about such drills because its air force is one of the weakest links in its military, which lacks high-tech jets and properly trained pilots.

The tests included an intercontinental ballistic missile and another shorter-range projectile that crossed the de facto maritime border and landed near South Korean territorial waters for the first time since a ceasefire ended hostilities in the Korean War in 1953.

Seoul and Washington have been warning for months that Pyongyang is ready to conduct another nuclear test at any time.

Sunday's joint statement stressed that "the path to dialogue remains open", urging North Korea to return to negotiations.

- Xi meeting -
 

Kim met three times with Biden's predecessor Donald Trump but failed to reach a lasting accord.

Washington has stuck by its twin-track approach of pressure and offers of talks.

US officials say North Korea has shown no interest in talks and, privately, some think it may be in one of its periodic cycles of escalation and that there is no choice but to wait.

The Sunday statement, dubbed the "Phnom Penh Declaration", included a pledge to work to boost deterrence.

"The Leaders intend to share DPRK missile warning data in real time to improve each country's ability to detect and assess the threat posed by incoming missiles," it said.

When Biden meets Xi on the sidelines of the G20 summit on the Indonesian island of Bali on Monday, he is expected to warn Xi that further North Korean missile and nuclear build-up would mean the United States boosting its military presence in the region -- something Beijing bitterly opposes.

"North Korea represents a threat not just to the United States, not just to (South Korea) and Japan but to peace and stability across the entire region," US National Security Advisor Jake Sullivan told reporters.