The United States highlighted its focus on close trilateral security coordination with South Korea and Japan on Monday, criticizing North Korea's recent cruise missile launches as "deeply destabilizing."

Pyongyang has conducted four rounds of cruise missile launches this year, including the test-fire of a submarine-launched ballistic missile, amid questions over how to rein in such cruise missile launches that are not subject to UN Security Council resolutions.

"These kinds of actions by the DPRK are deeply destabilizing and they are unhelpful and they contribute to greater risk in the region," State Department Deputy Spokesperson Vedant Patel said during a press briefing.

"We will continue to coordinate closely trilaterally with the ROK and Japan when it comes to pushing back on some of these malign and destabilizing actions," he added.

ROK and DPRK stand for the official names of South Korea and North Korea, the Republic of Korea and the Democratic People's Republic of Korea, respectively.

Patel also responded to a question about Russia's denial of arms trade with Pyongyang, vowing to keep close international coordination against weapons transfers between the two countries.

"What we do know is that there is a deepening relationship between the DPRK and Russia. We've seen that over the past many months, including that transfer of munitions from the DPRK to Russia," he said.

"We believe that these kinds of actions and activities are deeply concerning and destabilizing and we will continue to work in close coordination to fend off against those (actions)."

In a separate press briefing, Pentagon Press Secretary Major Gen. Patrick Ryder emphasized what he termed the "excellent" relationship between South Korea, the US and Japan, as the three countries jointly confront evolving North Korean threats.

"We will continue to share information as it relates to regional security and stability," he said.

In response to a question over whether the countries have "completely" tracked North Korean missile launches, he said, "We keep a very close eye on the region." (Yonhap)