The South Korea-United States alliance must be vigilant against North Korea's "persistent and proximate" threats as the country is developing its ballistic missile capabilities and readying for a fifth nuclear test, the top American commander here said Monday in his farewell ceremony.

"Just these last few days, we have witnessed attempts to develop ballistic missile capabilities, as well as claims North Korea will do a fifth nuclear test soon," Gen. Curtis Scaparrotti said in the South Korean Joint Chiefs of Staff-arranged ceremony to mark his departure from his current position.

The ceremony was held in the military training ground of the JCS in Yongsan, central Seoul.

"In the face of that, we cannot rest ... and we must be vigilant and ready, and I know that you will be," the outgoing general said. 

"Our combined strength is critical as we together face the dangerous, persistent, proximate threats from North Korea." 

Scaparrotti took office as the top commander of some 28,000 American troops stationed in South Korea in August 2013 and has recently been promoted to supreme allied commander of Europe.

Gen. Vincent Brooks, currently commander of the U.S. Army Pacific, has been nominated to succeed Scaparrotti.

During his near three-year term, Scaparrotti saw North Korean leader Kim Jong-un try to solidify his grip on power with high-profile military provocations, including land mine attacks in the heavily fortified Demilitarized Zone, which maimed two South Korean soldiers.

Earlier this year, North Korea conducted its fourth nuclear test and a long-range rocket launch, which has been condemned as a cover to test an intercontinental ballistic missile technology.

"We together as an alliance have successfully deterred North Korea, and we have proved our capabilities as we moved through the past 2 1/2 years," he said. "It is evident that we have never been stronger in our alliance." 

Against the evolving enemy and a changing strategic environment, the allies should also continue to adapt, improve and grow stronger, the general also said in his farewell speech.

During the ceremony, JCS Chairman Gen. Lee Sun-jin thanked Scaparrotti for the "deep faith and trust" he has fostered among South Koreans.

"Gen. Scaparrotti made the combined South Korea-U.S. forces into one team through the development of an operational plan that can meet future war environments on the Korean Peninsula and actual-warlike joint military exercises," Lee noted. 

Speaking to South Koreans in general, Scaparrotti said he and his wife "have loved our time here with you. We cherish this great people and your culture." (Yonhap)