HONG KONG—Facebook Inc. and its WhatsApp messaging service have suspended processing requests for user data from Hong Kong law-enforcement agencies following China’s imposition of a national-security law on the city.

WhatsApp is “pausing” such reviews “pending further assessment of the impact of the National Security Law, including formal human-rights due diligence and consultations with human-rights experts,” a WhatsApp spokeswoman said in response to a Wall Street Journal query on Monday.

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