South Korea supports US President Donald Trump's efforts to resume dialogue with North Korea, but aims to ensure its security posture is not weakened and that Seoul is not sidelined, South Korea's national security adviser said on Friday.

Seoul believes the resumption of talks between the US and North Korea should focus on progress on the North Korean nuclear weapons issue and must not undermine the country's security readiness, Wi Sung-lac told reporters.

"One point to keep in mind is the need to coordinate with the United States to ensure that any resumption of US-North Korea dialogue leads to substantive progress on the North Korean nuclear issue, alongside efforts to establish a peace regime on the Korean Peninsula," Wi said.

To achieve these aims, policy coordination and communication between South Korea and the United States were more important than ever, he said.

Wi cited Trump's order earlier this month to substantially scale back major joint military drills between the two allies, saying the US president was signaling a willingness to engage with North Korea.

At the same time, Seoul should ensure it was not "sidelined" in Washington's efforts to restart talks with Pyongyang, Wi said.

Trump cited in part Seoul's refusal to offer help in the Iran war for cutting short the Ulchi Freedom Shield drills this month and said they sent a wrong message to North Korea. Trump has been seeking a new summit with North Korean leader Kim Jong Un.

The two met three times in 2018 and 2019.