HONG KONG—China’s arrest of twelve Hong Kong professional-democracy activists, nabbed as they attempted to flee the city by boat in the experience of an intensifying crackdown on dissent, is fueling a new war of words and phrases between Washington and Beijing.

On Sunday, Chinese Overseas Ministry spokeswoman Hua Chunying said on Twitter that the people today detained weren’t looking for democratic freedoms but “elements trying to different Hong Kong from China.” Other Chinese officers this weekend accused the U.S. of meddling in China’s inside affairs.