The US Supreme Court has ruled President Trump's administration can enforce a ban on refugees.

Their temporary decision means the controversial restrictions can remain in force while an appeal is considered by a federal appeals court in San Francisco.

Supreme Court justices, however, rejected an attempt by the Trump administration to block a judge's ruling that stopped his travel ban on people from six Muslim-majority countries from being applied to the grandparents of US citizens.

Their decision was not unanimous, and three conservatives on the court of nine justices had noted that they would have granted the President's request in full.

In June, the Supreme Court had ruled that the travel ban could take effect - however, it could not be enforced on those with a "bona fide relationship" to an American citizen.

The judges did not define what would constitute such a relationship, but said it could include people with a close relative in the States, someone with a job offer, or a student who has been admitted to an American college or university.

Trump's administration narrowly interpreted this - and said a parent, spouse, sibling, son, daughter, son-in-law or daughter-in-law would be exempt from the ban.

But last week, US district judge Derrick Watson said grandparents, grandchildren, brothers and sisters-in-law, nieces, nephews, aunts, uncles and cousins should also count as a "bona fide relationship" - limiting the scope of the ban.

It is not clear how quickly the federal appeals court in San Francisco will return a ruling.