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The Trump administration has instructed organizations in other countries to stop disbursing H.I.V. medications purchased with U.S. aid, even if the drugs have already been obtained and are sitting in local clinics.

The directive is part of a broader freeze on foreign aid initiated last week. It includes the President’s Emergency Plan for AIDS Relief, the global health program started by George W. Bush that is credited with saving more than 25 million lives worldwide.

The administration had already moved to stop PEPFAR funding from moving to clinics, hospitals and other organizations in low-income countries.

Appointments are being canceled, and patients are being turned away from clinics, according to people with knowledge of the situation who feared retribution if they spoke publicly. Many people with H.I.V. are facing abrupt interruptions to their treatment.

But most federal officials are also under strict orders not to communicate with external partners, leading to confusion and anxiety, according to several people with knowledge of the situation.

U.S. officials have also been told to stop providing technical assistance to national ministries of health.