The US Supreme Court has allowed President Donald Trump to broadly implement a ban on refugees entering the country from around the world.

The Supreme Court justices granted on Tuesday a request from the Trump administration to block a lower court decision that would have eased the restrictive refugee policy and, according to the justice department, allowed up to 24,000 additional refugees to enter the United States before October.

The Supreme Court ruling gives Trump a partial victory as it prepares for a key hearing on the constitutionality of Trump's controversial executive order in October.

Trump signed a revised executive order on March 6 that banned travellers from six Muslim-majority countries - Iran, Libya, Somalia, Sudan, Syria and Yemen - for 90 days and locked out most refugees for 120 days in a move that the Republican president argued was needed to prevent "terrorist" attacks.

The March order followed an even stricter version in January, which was quickly challenged in court and suspended in February.

The administration has yet to say whether it will seek to renew the bans, make them permanent, or expand the travel ban to other countries.

Since being introduced in March, US courts have limited the scope of the revised executive order.

Lower courts have ruled that the bans violate the US Constitution and federal immigration law.

The high court has agreed to review those rulings.

Its intervention so far has been to evaluate what parts of the policy can take effect in the meantime.

The justices said in June that the administration could not enforce the bans against people who have a "bona fide" relationship with people or entities in the US. The justices declined to define the required relationships more precisely.

In a ruling last week, the 9th US Circuit Court of Appeals said grandparents, aunts, uncles and cousins of legal US residents would be exempt from the travel ban.

The justice department opted not to appeal that part of the 9th Circuit decision.

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However, the 9th Circuit also ruled that Trump's refugee policy was too broad, and the court allowed entry to refugees from around the world if they had a formal offer from a resettlement agency.

The justice department appealed, and the full Supreme Court sided, at least for now, with the administration in a one-sentence order.

A representative for the Hawaii attorney general, who challenged the administration in court, could not immediately be reached for comment.

Earlier on Tuesday, Hawaii said in a court filing that the US government could still "bar tens of thousands of refugees from entering the country".

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All the 9th Circuit ruling did is "protect vulnerable refugees and the American entities that have been eagerly preparing to welcome them to our shores", the state's lawyers said.

Amnesty International, the UK-based rights organisation, called Tuesday's Supreme Court decision a "devastating blow".

"The Supreme Court today has dealt yet another devastating blow to vulnerable people who were on the cusp of obtaining safety for themselves and their families," Amnesty's Naureen Shah said in a statement.

"They [refugees] continue to be subjected to unimaginable violence and fear while their lives are in limbo.

"This ban is inherently cruel and no part of it should be allowed to stand."