The Tumen River forms the North's border with China, and Pyongyang has been installing electric fencing and strengthening border controls there since late 2015, according to a report from the Korea Institute for National Unification, a think tank funded by the South Korean government.
Exports rose 11.3 percent in June in dollar terms, the customs administration said Thursday.
"We hope all relevant sides can make sure that they are clear that Security Council sanctions imposed on North Korea are not comprehensive economic sanctions", Shuang said.
After North Korean leader Kim Jong-un took power in 2011, the number of North Koreans fleeing to the South dropped annually, falling from two-thousand-706 in 2011 to one-thousand-502 in 2012.
In March of a year ago, China agreed to enforce United Nations sanctions after North Korea launched a missile with potential nuclear capabilities. They argue against disrupting trade in food and other goods that might cause public hardship.More news: Monopoly maker says retailers didn't buy Rey
China has slashed imports of coal from North Korea even as overall trade between the countries continues to rise.
Statistics compiled by Seoul's Unification Ministry show that the number of North Koreans entering South Korea has decreased by a fifth (20.8 percent) in the first half of 2017 compared to the same period previous year.
Imports from North Korea actually fell 13.2 percent to $880 million, it said, but exports to the pariah state jumped 29.1 percent to $1.67 billion. Huang said month-on-month figures showed an even sharper decline.
The UN and the USA have attempted to use sanctions for the past decade in an attempt to stem North Korea's nuclear weapons development, but the latest July 4 test, which demonstrated a significant advance in its capabilities, have forced global bodies to reconsider their response going forward.