In another setback for President Donald Trump, a federal judge in Hawaii has further weakened his already diluted travel ban by vastly expanding the list of family relationships with US citizens that visa applicants can use to get into the US.

Key points: The 'travel ban' tightens already-tough visa policies for people from six Muslim-majority countries

The 'travel ban' tightens already-tough visa policies for people from six Muslim-majority countries Relatives of people with visas are exempt from the travel ban

Relatives of people with visas are exempt from the travel ban The definition of a relative has been broadened

The ruling is the latest piece of pushback in the fierce fight set off by the ban Mr Trump first attempted in January. It will culminate with arguments in front of the US Supreme Court in October.

The current rules are not so much an outright ban as a tightening of already-tough visa policies affecting citizens from six Muslim-majority countries: Syria, Sudan, Somalia, Libya, Iran and Yemen.

People from those countries who already have visas will be allowed into the country. Only narrow categories of people, including those with relatives named in the ruling, will be considered for new visas.

US District Judge Derrick Watson on Thursday ordered the Government not to enforce the ban on grandparents, grandchildren, brothers-in-law, sisters-in-law, aunts, uncles, nieces, nephews and cousins of people in the United States.

"Common sense, for instance, dictates that close family members be defined to include grandparents," Judge Watson said in his ruling.

"Indeed grandparents are the epitome of close family members."

US District Judge Derrick Watson expanded the list of family relationships needed by people seeking new visas. ( AP: George Lee/The Star-Advertiser )

Judge Watson also ruled that the Government may not exclude refugees who have formal assurance and promise of placement services from a resettlement agency in the US.

The US Supreme Court, which last month allowed a scaled-back version of the ban to go into effect before it hears the case in October, exempted visa applicants from the ban if they can prove a "bona fide" relationship with a US citizen or entity.

The Trump administration defined "bona fide" relationship as those who had a parent, spouse, fiance, son, daughter, son-in-law, daughter-in-law or sibling already in the US.

The case came back to Judge Watson when the 9th US Circuit Court of Appeals ruled he had the authority to interpret the Supreme Court's order and block any violation of it.

Hawaii Attorney-General Douglas Chin, who represents the state as the plaintiff in the case, said the court made clear "that the US Government may not ignore the scope of the partial travel ban as it sees fit".

"Family members have been separated and real people have suffered enough," Mr Chin said in a statement.

The Supreme Court ruled that workers who accepted jobs from American companies, students who enrolled at a US university or lecturers invited to address a US audience would also be exempt.

A relationship created for purposes of avoiding the travel ban would not be acceptable, the justices said.

Mr Trump had proposed a blanket ban on Muslims during his presidential campaign, but later limited it to a handful of countries when he issued his initial travel ban in January, promoting it as a necessary tool for national security and fighting terrorism.

It set off massive protests at airports around the country and immediately sparked a sprawling, ongoing legal fight.

Sorry, this video has expired Activists protest Trump's 'racist, unconstitutional' ban on Muslim-majority nationals entering the US

Courts blocked that first ban as well as a second the Trump administration had retooled, until the Supreme Court partially reinstated it at the end of June.

It is unclear how significantly the new rules have affected or will affect travel. In most of the countries singled out, few people have the means for leisure travel. Those that do already face intensive screenings before being issued visas.

AP