China's chief envoy for North Korean affairs says the reasons he hasn't visited Pyongyang are "complicated" but that China remains committed to finding a diplomatic solution to tensions over the North's nuclear weapons program.

Vice Foreign Minister Kong Xuanyou (SHWEN'-yo) offered no details Friday but the lack of a visit has been cited as an indication of the much deteriorated state of relations between Beijing and Pyongyang.

China has long been the North's chief economic partner and political ally but the North's refusal to rein in its actions has left Beijing officials increasingly frustrated.

China's support for increasingly tough United Nations sanctions has also sparked a backlash from Pyongyang.

The last high-level Chinese visitor to Pyongyang was Song Tao, head of the ruling Communist Party's International Department, in November.