Chinese companies have not leased piers at a port of North Korea's free trade zone, a Pyongyang official has told Hong Kong media, raising speculation that the shock execution of the North Korean leader's uncle might have soured business ties with its key ally. China reportedly agreed to invest about US$3 billion in developing the free trade zone in North Korea's northern tip of Rason, formerly known as Rajin and Sonbong, in late 2011. The special trade zone sits across the border from China's northeastern Jilin province.