Chinese police tightened controls across Inner Mongolia on Sunday following a week of ethnic protests over the hit-and-run killing of a Mongolia herder by a Chinese truck driver, the Wall Street Journal reported. The protests, which began on May 23, peaked on Wednesday as 2,000 ethnic Mongolian students took to the streets in Xilinhot, according to UK-based rights group Amnesty International. Authorities required students to obtain permission and register before leaving university campuses, and had also blocked searches for terms including “Inner Mongolia” on Sina Weibo, the popular microblogging service. According to rights groups, at least 18 protestors were injured and 40 were detained by police last week. Inner Mongolia, where ethnic Mongolians make up roughly 20% of the total population, has largely avoided the unrest that has plagued China’s Tibetan and Muslim regions. With a population of only 24 million, Inner Mongolia is one of China’s fastest-growing regions economically due to its vast reserves of coal, rare-earths elements, and other natural resources.