US Ambassador Harry Harris has said that South Korea and the United States had fought together against "invasion from the north" during the Korean War, amid a controversy over Chinese President Xi Jinping's characterization of the conflict as the fight against US "imperialist invaders."

Harris made the remarks at an anniversary event for the Korea Times on Thursday, as he stressed the two countries' fight for democracy under the alliance, which he said was "forged in blood in the crucible of war."

Last Friday, Xi cast the war as the fight against what he termed imperialist invaders during a speech to mark the 70th anniversary of China's participation in the 1950-53 conflict that Beijing refers to as the fight to "resist US aggression and aid Korea."

"Our two nations' commitment and resolve to democracy was put to the test as we fought side by side with the sending states against invasion from the North," he said according to a transcript posted on the website of the US Embassy in Seoul.

"Our fight to protect the right of this Republic to determine its destiny continues to shape the partnership between the United States and the Republic of Korea today," he added.

Following the controversy over Xi's characterization of the Korean War, Seoul's foreign ministry reiterated that the "undeniable historical fact" was that the war was caused by North Korea's invasion.

The war, the first major armed conflict of the Cold War, broke out after North Korean troops invaded the South on June 25, 1950, with backing from China and the then Soviet Union. It ended in a truce rather than a peace treaty, leaving the two Koreas technically at war. (Yonhap)