The Pakistani government has protested the arrest in the United States of a man accused of acting as a Pakistani agent to influence Washington policymakers on the disputed Himalayan region of Kashmir.

Pakistan said Thursday it had registered its concerns at the U.S. embassy in Islamabad and accused the United States of a slander campaign against Pakistan.

Kashmiri separatists strongly condemned Syed Ghulam Nabi Fai's arrest. Separatist leader Syed Ali Geelani said it was carried out “at the behest of India” as part of a diplomatic conspiracy. He and other separatists called a strike in Indian-controlled Kashmir on Friday to protest the arrest.

U.S. authorities detained Fai, the executive director of the Kashmiri American Council, on Tuesday and charged him with conspiracy. A second man, Zaheer Ahmad, was also charged and is believed to be in Pakistan.

The U.S. Department of Justice says Fai lobbied U.S. lawmakers on Kashmir using $4 million from the Pakistani government, including the country's military spy agency.

But Islamabad says Fai's organization has been working toward “upholding [the] fundamental rights of Kashmiris.”

As head of the Kashmiri American Council, Fai advocated against Indian rule in Kashmir, which is divided between India and Pakistan, but claimed by both. Rebel groups have been fighting since 1989 for the region's independence or its merger with Muslim-majority Pakistan. The violence has left more than 47,000 people dead.