North Korea is "always welcome" at the negotiating table even though the threat of further provocation may be looming, Japan's nuclear envoy, Takehiro Funakoshi, said on Wednesday ahead of a meeting with his U.S. and South Korean counterparts.

The three nations, which met in Tokyo to discuss their North Korea strategy, are tightening security cooperation as tension rises in the wake of recent North Korean moves such as an unusual number of missile launches and warnings from the United States that Pyongyang could sell weapons to Russia.

Wednesday's meeting came after trilateral talks held over the past two months, including a gathering of security advisers from the three nations in Hawaii last week amid signs North Korea may be about to conduct its first nuclear test since 2017.

"North Korea is continuing and even accelerating its nuclear and missile capabilities, and there is a looming chance of further provocation, including a nuclear test," Funakoshi said before the discussions.

"At the same time, we remain open to entertaining dialogue with North Korea," he said, adding that Pyongyang was always welcome at negotiations - a sentiment counterparts Sung Kim from the United States and Kim Gunn from South Korea echoed.

North Korea has conducted missile tests at an unprecedented pace this year.

In mid-August, North Korea fired two cruise missiles from its west coast after South Korea and the United States resumed their largest field exercises in years. Pyongyang has long denounced the exercises as a rehearsal for war.

South Korea's national security adviser, Kim Sung-han, said after the Hawaii meeting that he and his counterparts had agreed there would not be a "soft" response if North Korea conducted a nuclear test. He did not give details, but the government has previously mentioned more sanctions.

An additional concern is that North Korea may sell arms to Russia, its old Cold War ally.

The White House said on Tuesday that Russia could be about to buy "literally millions" of artillery shells and rockets from Pyongyang, but that it had no indication that the purchase had actually occurred.