During his two-day visit, National Security Office chief Chung Eui-yong will meet with US counterpart HR McMaster and other officials and also schedule a meeting between Moon and US President Donald Trump in Washington later this month.
Durbin is a ranking member of the Senate Committee on Appropriations and therefore has a say in how the US spends its defense budget.
South Korean President Moon Jae-in's top security aide left for Washington on Thursday as the new leader tries to reassure his country's main ally he will not scrap a deal to host a missile defence system that has angered China.
Two launchers are already in operation at the THAAD base in Seongju, North Gyeongsang Province, some 300 kilometers southeast of Seoul.
The presidential Blue House said on Wednesday the Defence Ministry had intentionally omitted details about the THAAD battery in a report made to Chung last week, when the government was preparing for the summit.
After the decision was taken in Seoul, Beijing retaliated with undeclared economic sanctions, targeting South Korean businesses depending on China.
Since South Korea and the USA jointly announced their decision to deploy a THAAD battery in July past year, controversy has been growing over its efficiency, possible fallout on Seoul's relation with China, environmental and health impacts, and alleged murky processes of decision making and implementation. "We are working transparently in unison with the Republic of Korea to defend against the growing threats imposed by North Korea's aggressive and destabilizing nuclear ballistic missile and nuclear programs", he said.
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The defense expert added: "There is no harm in having the THAAD system in place".
"The focus of the issue of THAAD deployment, is that there was a lack of public discussion that included the right of the people to know", said ministry spokesman Cho Jun-hyuk.
"President Moon told the defense ministry to carry out the due process to evaluate the environmental impact as required by the law to secure the procedural legitimacy of the deployment that every citizen could accept", he said.
There were suggestions at one point that the new launchers were brought into South Korea by the US military without knowledge of the Seoul government.
According to Kazianis, "North Korea has over 1,000 missiles that literally could strike South Korea at any time".
China has denied it had discriminated against South Korean companies, which have faced product boycotts and bans on Chinese tourists visiting South Korea. Topping the agenda, of course, were foreign policy and national security.
"I think that requires making it clear to Kim Jong-un that there is a price to pay for his aggressive development of missiles and nuclear weapons", he added.