Sen. John McCain (R-AZ), chairman of the Senate Armed Services Committee, and Sen. Jack Reed (D-RI), the committee's ranking member, also issued a joint statement congratulating Moon on the election win.

"While South Korea has been through a difficult time over the past several months, we hope that the inauguration of a new president, popularly elected by the people of South Korea, will allow the country to emerge with renewed strength and vigor," the senators said.

"With threats in the region escalating, it is vital that the United States and South Korea continue to work together. The South Korean people should know that the US remains firmly committed to a strong alliance between our countries," they said. 

They also said they look forward to "working with President Moon to strengthen security cooperation."

Rep. Ed Royce (R-CA), chairman of the House Foreign Affairs Committee, also welcomed Moon's election, saying the US has no better partner in the Asia-Pacific than South Korea.

"I look forward to working with President-elect Moon's government to maintain peace and stability on the Korean peninsula and in the region," Royce said. ""As chairman of the House Foreign Affairs Committee, I am committed to strengthening the US-Korea partnership so the two nations can promote prosperity, peace, stability, and respect for human rights."

Sen. Ben Cardin (D-MD), ranking member of the Senate Foreign Relations Committee, praised South Korea for demonstrating to the world through Tuesday's election that the country is "a vibrant democracy with a robust civil society and strong institutions."

"Our alliance with the Republic of Korea is one of the most important relationships the US has in the world today, nurtured by shared sacrifice, common values, and mutual security and economic interests," the senator said. "I look forward to working with President-elect Moon to more closely cooperate on a number of issues pertinent to the security and well-being of both our peoples, including resolving the North Korea situation diplomatically."

Sen. Cory Gardner (R-CO), chairman of the Senate Foreign Relations Subcommittee on East Asia, said the alliance between the two countries was "forged in blood."

"I want to extend my congratulations to the South Korean people and to President Moon Jae-in," Gardner said. "The US and the Republic of Korea alliance is forged in blood and the bonds of our friendship are unbreakable. I look forward to working with President Moon to strengthen our security, economic, and diplomatic ties."

The four co-chairs of the Congressional Caucus on Korea -- Reps. Peter Roskam (R-IL), Gerry Connolly (D-VA), Mike Kelly (R-PA), and Ami Bera (D-CA) -- also issued a joint statement.

"We extend our sincere congratulations to President-Elect Moon Jae-in and wish him and his administration well in the months and years ahead as they prepare to lead the Republic of Korea, a key and indispensable US ally, through the many challenges facing the Korean Peninsula," the statement said.

"As co-chairs of the Korea Caucus, we remain steadfastly committed to defending and strengthening the US-Korea alliance. Our relationship was forged on the battlefield nearly seven decades ago and now forms a lynchpin of US foreign policy in the Asia Pacific region," it said. (Yonhap)