The US Justice Department asked the Supreme Court to block the latest federal ruling scaling back President Donald Trump's restrictions on citizens from the six Muslim-majority countries entering the United States.

It comes after Hawaii federal Judge Derrick Watson expanded the type relatives of a US person or entity that will be allowed to travel to the United States.

The decision added grandparents and grandchildren among others to the list of those exempt from the ban, which previously included parents, spouses, children, sons- and daughters-in-law, siblings and step- or half-siblings.

It marked the latest setback to Trump's attempt to impose an outright ban on a number of Muslims entering the US. The order has already been scaled back after months of legal wrangling between the government and several US courts.

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In a statement, US Attorney General Jeff Sessions said that the White House would "reluctantly return directly to the Supreme Court" to overturn the Hawaii district court's decision.

"By this decision, the district court has improperly substituted its policy preferences for the national security judgments of the executive branch in a time of grave threats, defying both the lawful prerogatives of the executive branch and the directive of the Supreme Court," Sessions said.

Interpreting the ban

The White House's original order, enacted in January, imposed a 90-day ban on all citizens from Iraq, Iran, Libya, Somalia, Sudan, Syria, and Yemen from traveling to the US. It also blocked all refugees from entering the country for 120 days.

While the White House claimed that the ban was necessary for national security and to combat terrorism, courts blocked the ban on discriminatory grounds. A second revised ban, which exempted citizens from Iraq, was also blocked until the Supreme Court partially reinstated it last month, with the exception of people with a "bona fide relationship" to the United States.

The court's language left it somewhat open to interpretation who has a credible claim to enter the United States.

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The Trump administration defined that to mean parents, spouses, children, sons- and daughters-in-law, siblings and step- and half-siblings.

However, Judge Derrick Watson's ruling Hawaii expanded that list include grandparents, grandchildren, brothers-in-law, sisters-in-law, aunts, uncles, nieces, nephews and cousins.

The case came back to Watson after the 9th US Circuit Court of Appeals ruled that he had authority to interpret the Supreme Court's decision.

"Common sense, for instance, dictates that close family members be defined to include grandparents," Watson said. "Indeed grandparents are the epitome of close family members. The government's definition excludes them. That simply cannot be."

Douglas Chin, Hawaii's attorney general who is representing the state as the plaintiff in the case, said the court had made clear "that the US government may not ignore the scope of the partial travel ban as it sees fit."

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"Family members have been separated and real people have suffered enough," he added.

Watson also ruled that citizens from the six Muslim-majority countries who had "bona fide" ties to the US - such as a job or acceptance into university - would also be permitted to enter.

The Justice Department could have chosen to challenge the Court of Appeals' decision to send the case back to Hawaii, but opted instead to take the case back before the Supreme Court.

The six countries affected by Trump's travel ban. Iraq has since been removed from the list.

Scaled back bans on refugees

The Hawaii court also ruled that refugees who had already been assured of a placement by a US resettlement agency would be exempt from the ban.

That ruling follows on from the Supreme Court's decision to uphold the order's 120-day ban on all refugees from the six affected countries, including an indefinite ban on refugees from Syria, unless they already have family living in the US.

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Such an assurance, Watson wrote, "meets each of the Supreme Court's touchstones: it is formal, it is a documented contract, it is binding, it triggers responsibilities and obligations, including compensation, it is issued specific to an individual refugee only when that refugee has been approved for entry by the Department of Homeland Security, and it is issued in the ordinary course, and historically has been for decades."

The Supreme Court is scheduled to review the overall case in October, by which time both bans will have run their course.

dm/rt (AP, AFP, dpa)