North Korea did not import any crude oil from China in January, marking the first absence of monthly deliveries from China in five months, a Seoul government report showed Monday. It was not immediately clear whether the January absence of crude shipments to North Korea from China was linked to Beijing's growing frustration with Pyongyang over its nuclear program, but it followed the execution of the once-powerful uncle of North Korean leader Kim Jong-un last December. China, North Korea's key ally and economic lifeline, has been in a delicate position because the executed uncle, Jang Song-thaek, was considered a supporter of China-style reforms to revive the North's moribund economy and played an important role in dealing with economic projects with Beijing. Last year, monthly shipments of crude oil from China to North Korea were absent in the months of February, June and July. However, annual shipments of crude oil to North Korea from China rose 11.2 percent on-year to 578,000 tons in 2013.