Twelve armed North Korean soldiers apparently defected across the border to China's Jilin Province earlier this month but were captured by Chinese troops and sent back to the North.

Late last month, two North Korean soldiers shot and killed their senior officer and fled to Jilin Province, prompting experts to suspect something unusual is going on in army units stationed along the border with China.

The 12 North Korean soldiers stationed with a border unit defected across the Chinese border in two groups but were sent back after being captured by Chinese troops, a diplomatic source in Beijing said Thursday.

Another source in the Chinese town of Yanji near the border with North Korea, said the other two North Korean soldiers shot and killed their senior officer and crossed over the border into Changbai, Jilin Province, causing Chinese troops nearby to scramble into emergency mode.