Semiconductor Manufacturing International Corp. retreated to a four-month low in Hong Kong after the U.S. imposed export restrictions on China’s largest chipmaker.

The shares slumped as much as 7.9 percent Monday, adding to their 25 percent loss for the month. Also listed in Shanghai, SMIC’s stock there retreated as much as 6.6 percent to the lowest level since its July debut. U.S. firms must now apply for a license to export certain products to the chipmaker, the Commerce Dept. said in a letter dated Sept. 25. SMIC and its subsidiaries present "an unacceptable risk of diversion to a military end use,” the department’s Bureau of Industry and Security wrote.

The U.S. stopped short of placing SMIC on the so-called entity list, which means the restrictions are not yet as severe as those imposed on China’s Huawei Technologies Co. Still, the ruling against the chipmaker marks a further escalation in the tensions between the world’s two most powerful countries that have already ensnared other Chinese tech companies including ByteDance Ltd. and Tencent Holdings Ltd.