An Qingxu
After Shi Siming's submission to Tang, the other nearby prefectures also largely submitted to Tang, leaving An Qingxu isolated in Yecheng, holding only Yecheng and its surrounding region. However, a number of Tang generals, including Li Guangbi and Zhang Gao, doubted Shi's sincerity. In summer 759, under Li Guangbi's advice, Emperor Suzong had Wu Cheng'en try to persuade Ashina Chengqing into killing Shi together and seizing Fanyang. Shi discovered this and put Wu to death. He did not initially formally turn against Tang, but made an ultimatum demanding Li Guangbi's death. Meanwhile, though, with An Qingxu seeking aid from him, he launched his troops and headed south toward Yecheng. Shi quickly captured Wei Prefecture (魏州, in modern Handan, Hebei) from the Tang general Cui Guangyuan (), and then declared himself "the Great Holy Prince of Yan" () in spring 760.