The soldier walked into the southern sector of the Demilitarized Zone under cover of darkness shortly before midnight on Tuesday, said a Defense Ministry official who identified himself only as Maj. Yoon.
The official declined to give other details, but said an announcement will be made after President Bush leaves Seoul early Thursday.
The national Yonhap news agency identified the North Korean as 22-year-old Pvt. Ju Sung Il. Ju carried with him two AK-47 rifles when he defected across the border, about 1,200 yards from Dorasan Train Station, where President Bush gave a speech on Wednesday.
President Bush's visit to the Korean DMZ.
The North Korean soldier fired seven warning shots before crossing the border, said Yonhap, citing an unidentified Defense Ministry source.
South Korean guards escorted the defector to safety and turned him over to investigators for questioning, Yonhap said.
The inter-Korean border is the world's most heavily armed and defections across it are relatively rare. There have been six defections across the land border since President Kim Dae-jung took office four years ago.
Most North Korean defectors complained about severe food shortages.
So far this year, 54 North Korean civilians have fled to the South by way of China. Last year, 583 North Koreans defected to the South, up from 312 in 2000.
The Koreas were divided in 1945. Some 37,000 U.S. soldiers are stationed in South Korea, a legacy of the 1950-53 Korean War.
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