Pakistan, Aug. 13 -- The United States has revoked more than 600 visas in the past month as part of a crackdown on birth tourism networks.

US Secretary of State Marco Rubio said the government is targeting organisations accused of exploiting immigration rules. He declared that American citizenship is not for sale.

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According to the State Department, criminal networks allegedly coach foreigners to misuse the visa system and falsify documents. Officials say these networks seek US citizenship for children born in America.

The department has established a Birth Tourism Prevention Task Force to identify and dismantle such operations. The task force will also review the activities ...