China has reduced "a significant amount" of its oil supplies
There are growing concerns that Pyongyang may be planning to follow up its recent missile launches with a nuclear test.
But North Korea will not rule out a nuclear test as long as Washington is hostile toward Pyongyang.
China, the communist North's closest ally and key provider of oil, has agreed with South Korea to cooperate to prevent a possible North Korean nuclear test.
China also has reduced "a significant amount" of its oil supplies to Pyongyang since the July 5 missile launches, South Korea's Chosun Ilbo newspaper said.