Meanwhile, Yanqi had remained friendly with Tang, but in or before 644, the Western Turkic general Ashina Quli (阿史那屈利) had taken the Yanqi king Long Tuqizhi's daughter to be his brother's wife, and, in response, Long Tuqizhi began to favor the Western Turkic Khaganate and decreased its tributes to Tang. Guo Xiaoke requested permission to attack Yanqi, and in 644 Emperor Taizong approved. It happened at the time that three of Long Tuqizhi's brothers were at Xi Prefecture, and Guo made one of them, Long Lipozhun (龍栗婆準) his guide. It was said that because Yanqi's capital was surrounded by water, it took little precautions against an attack, and Guo made a surprise attack, crossing the waters at night. In the morning, the Tang soldiers climbed the walls of Yanqi, capturing it and Long Tuqizhi. Guo put Long Lipozhun in charge of Yanqi's affairs and withdrew. Three days later, Ashina Quli arrived with a relief force, but Guo had already withdrawn; he therefore seized Long Lipozhun and chased after Guo, who struck back and stopped his advance.