The decision to delay the training was made after Seoul declared its highest "severe" alert level over the virus, Combined Forces Command said, adding the postponement was "until further notice".

The United States has 28,500 troops in South Korea to protect it against the nuclear-armed North, many of them based south of Seoul at Camp Humphreys in Pyeongtaek -- Washington's biggest overseas military facility.

The security allies have previously scaled back their annual joint military exercises significantly to facilitate nuclear talks with Pyongyang -- which condemns such drills as preparations for an invasion -- but a command coordination exercise had been planned for this spring.

South Korea has the highest number of virus cases in the world outside China, where the disease first emerged in December.

No new deaths had occurred, the Korea Centers for Disease Control and Prevention said in a statement, with the toll at 12.