SEOUL, Aug 28 (Reuters) - South Korea supports U.S. 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 U.S. 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 U.S.-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 U.S. 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.

South Korea, Japan and the ​United States will conduct joint military ​drills from September 9 to 11 to test readiness against North ‌Korea's missile and nuclear weapons threats, South ​Korea said on Friday.

Wi ​said South Korea is seeking to deepen cooperation with Washington on a range of issues that have sometimes caused friction between the allies.

These include South Korean investment ​in the U.S. agreed ‌under a trade deal, the treatment of U.S.-listed e-commerce firm Coupang, security cooperation, ​intelligence sharing and the transfer of wartime operational control, he said.

(Reporting by Jack ​Kim and Heejin KimEditing by Ed Davies)