Washington DC - A federal judge has struck down a government ban on visas to nationals from 75 countries who wish to settle in the country indefinitely, dealing a blow to President Donald Trump's immigration crackdown.

In a ruling issued on Friday in the Southern District of New York, Judge Jeannette Vargas called the policy "contrary to law" and said Secretary of State Marco Rubio had exceeded his "statutory authority" in issuing it.

The policy, which came into force in January, suspended the processing of immigrant visas to nationals of 75 countries, including Afghanistan, Brazil, Egypt, Iran, Iraq, Nigeria, Somalia, Thailand, and Yemen.

At that time, the State Department had said the decision was made "to ensure that immigrants from high-risk countries do not unlawfully utilize welfare in the United States or become a public charge."

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But Vargas ruled that consular officers were wrongly ordered to refuse immigrant visas solely based on an applicant's country of origin, even if they had determined the applicant was otherwise.

Friday's ruling vacates any visa denial based solely on the policy.

The government can appeal the ruling.

Trump campaigned on a promise to expel millions of undocumented migrants and has taken a number of aggressive and controversial actions since returning to office, aimed at speeding up deportations and reducing border crossings.