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By Arshad Mohammed and Yeganeh Torbati

WASHINGTON, June 28 (Reuters) - Visa applicants from six Muslim-majority countries must have a close U.S. family relationship or formal ties to a U.S. entity to be admitted to the United States under guidance distributed by the U.S. State Department on Wednesday.

The guidance defined a close familial relationship as being a parent, spouse, child, adult son or daughter, son-in-law, daughter-in-law or sibling, including step siblings and other step family relations, according to a copy of a cable distributed to all U.S. diplomatic posts and seen by Reuters.

The cable, first reported by the Associated Press, said close family "does not include grandparents, grandchildren, aunts, uncles, nieces, nephews, cousins, brothers-laws and sisters-in-law, fiancés, and any other 'extended' family members."

It also specified that any relationship with a U.S. entity "must be formal, documented, and formed in the ordinary course, rather than for the purpose of evading the E.O.," a reference to U.S. President Donald Trump's March 6 executive order barring most U.S. travel by citizens of the six nations for 90 days.

The cable provides advice to U.S. consular officers on how to interpret Monday's Supreme Court ruling that allowed parts of the executive order, which had been blocked by the courts, to be implemented while the highest U.S. court considers the matter.

The six nations whose citizens are covered by the executive order are Iran, Libya, Somalia, Sudan, Syria, and Yemen.

Asked about the guidance issued on Wednesday night, the State Department declined to comment on internal communications.

The cable's language closely mirrored the Supreme Court's order on the travel ban, though it appeared to interpret it in a narrow manner, notably in its definition of close family.

It was unclear on Wednesday evening whether the State Department's interpretation of the court's order would spark further legal action by opponents of the ban.

The guidance gave several examples of what might constitute a bona fide relationship with a U.S. entity, and said broad categories would be exempt from the travel ban, such as those eligible for student visas, "as their bona fide relationship to a person or entity is inherent in the visa classification."

Similarly, those eligible for family or employment based immigrant visa applications are exempt from the travel ban, the cable said.

The cable said "a worker who accepted an offer of employment from a company in the United States or a lecturer invited to address an audience in the United States would be exempt" from the travel ban, but someone who simply made a hotel reservation would not count as someone with a bona fide relationship.