North Korea complained to the United Nations on Monday about joint military exercises by the United State and South Korea, describing it as "the worst ever situation" because USA nuclear war equipment had been deployed ready to strike.
"The government has kept the stance (over the need to support those in need in North Korea) on humanitarian grounds, but it also takes into account various factors for the provision of the aid at an appropriate time", said an official at Seoul's unification ministry.
Over the decades since the peninsula was divided, dozens of North Korean soldiers have fled to the South through the DMZ, which extends for two kilometers either side of the actual borderline.
The US Navy ended President Donald Trump's trip to Asia with a bang by having three aircraft carriers drill with South Korean and Japanese navy ships in the Pacific in a clear message to North Korea.
There was no immediate comment on the incident from North Korea.
The defector's rank was not immediately clear.
The man, identified only as a 58-year-old from Louisiana, had arrived in South Korea last week and wanted to enter the North for "political purposes", but was reported by a local villager, Yonhap said.
Two North Korean soldiers defected to the South in June after crossing the frontier at another location.
These were the first gunshots fired at the truce village of Panmunjom in 33 years and the first defection of a North Korean soldier since 2007.
At Panmunjom, once an obscure farming village inside the 2 1/2-mile-wide DMZ that separating the rivaling countries, North Korean soldiers wearing lapel pins with the images of late North Korean leaders often use binoculars to monitor visitors from the South.
North Korea conducted its sixth and most powerful nuclear bomb test on September 3, but has not launched any missiles since firing one over Japan on September 15, the longest such lull this year.