A US appeals court on Monday left in place a block on President Donald Trump's travel ban targeting citizens from six Muslim majority nations -- the latest in a string of judicial blows for the controversial measure.

The US Court of Appeals for the Ninth Circuit in its ruling largely upheld an injunction on the ban issued by a lower court, but said the government was within its right to review the vetting process for people entering the country.

"Immigration, even for the president, is not a one-person show," the three justices said in their unanimous ruling. "The president, in issuing the executive order, exceeded the scope of the authority delegated to him by Congress."

The decision came just ahead of a deadline for states challenging the ban to submit briefings before the US Supreme Court in response to the Trump administration's request that the nine justices hear the case.

The US Justice Department filed an emergency application to the Supreme Court on June 1, urging it to undo two lower court rulings blocking Trump's decision to prevent entry to travelers from Iran, Libya, Somalia, Sudan, Syria and Yemen for 90 days.

Trump's executive order also temporarily puts a halt to America's refugee program and reduces the number of refugees to be admitted this year to 50,000, instead of the 110,000 planned by the Obama administration.

The Trump administration argues the measures are needed to ward off terrorist attacks in the country while the government reviews its vetting process.

Critics say the ban is discriminatory and violates the US constitution by specifically targeting Muslim-majority countries.

The Justice Department declined to comment on the latest ruling.

- Powers not 'unlimited' -

The Ninth Circuit Court of Appeals appeared to reject much of the administration's arguments for reinstating the travel ban, notably relying on government reports to support its decision.

Its ruling said that a report from the Department of Homeland Security issued just after Trump's first executive order in March concluded that citizenship of any given country "is unlikely to be a reliable indicator of potential terrorist activity."

Quoting the report, it added that citizens from the countries targeted by Trump's ban are "rarely implicated in US-based terrorism."

It also rejected the government's assertion that Trump's executive order -- which was revised after the initial one was struck down by the courts -- was not subject to judicial review.

"Although the executive order has broad discretion over the admission and exclusion of aliens, that discretion is not boundless," the court said.

"Whatever deference we accord the president's immigration and national security policy judgments does not preclude us from reviewing the policy at all," it added.

It said while the president has broad powers to suspend the entry of aliens, that authority is not "unlimited."

The state of Hawaii, one of the jurisdictions challenging the ban, said in court papers filed Monday before the Supreme Court that Trump's order had had "staggering" consequences. It said reinstating it would plunge "the country back into the chaos and confusion that resulted when the first (executive order) was announced."