Chinese Vice Foreign Minister Liu Zhenmin arrived Monday in North Korea, making him the first high-ranking Chinese official to visit since February, Reuters reported. The purpose of the visit was to discuss border issues, according to the North Korean state-run Korean Central News Agency.

The news comes the same day as North Korea rejected calls by the U.S. and U.N. to increase sanctions in response to Pyongyang’s missile and nuclear tests in September. North Korean officials called sanction resolutions “illegal criminal documents” and blamed a U.S.-orchestrated conspiracy. China, Pyongyang’s most important ally, agreed to sign on to the most recent round of sanctions and is being pressured by the U.S. to implement even stricter measures.

Relations between China and North Korea have seemingly grown increasingly tense since North Korean leader Kim Jong Un took power after his father's death. Earlier this year, Victor Cha of the U.S.-based Center for Strategic and International Studies led a team of researchers to observe satellite imagery of the border. His team concluded that trade had significantly decreased and that it was likely China was cutting the flow as punishment for a nuclear test conducted by North Korea in January.

614786208 Frontier sign on the iron railing at border side of Chinese Dandong, from where tourists can overlook North Korea. Photo: Getty Images

China has not publicly acknowledged whether it is taking unilateral punitive actions against its neighbor or not. While some Chinese truck drivers who spoke to Reuters in September said nothing had changed, others claimed that moving goods between the two countries became a lot more difficult following this year’s new round of sanctions.

"The checks really stepped up after the sanctions were introduced earlier this year," a driver surnamed Wang told Reuters.

China and North Korea share an 880-mile border, divided by the Yalu River, Paektu Mountain and the Tumen River. The largest Chinese border city, Dandong is connected to the North Korean city of Sinuiju by the China Korean Friendship Bridge and represents the main trading hub for goods entering North Korea. While China is apparently often lax when it comes to trade in the city, Chinese authorities apparently clamped down in September on what they viewed as “serious economic crimes” committed by a prominent Chinese firm involved in selling industrial machinery and equipment to North Korea. The crackdown and massive investigation that followed has reportedly seriously affected trade between China and North Korea.

Zhenmin's visit comes as former U.S. officials met with North Korean diplomats in Malaysia over the weekend to discuss a possible peace deal. U.S. delegates included former Clinton administration negotiator Robert Gallucci, North Korea specialist Leon Sigal and former U.S. special envoy for North Korea Joseph DeTrani. Though the talks were informal, Sigal said they had made "progress."