Ruling on a case brought by the state of Hawaii, the appeal judges found that the executive order violated existing immigration legislation.

It is a further legal setback for the president's efforts to get the ban he promised his supporters.

Mr Trump criticised the San Francisco-based court's ruling.

"Well, as predicted, the 9th Circuit did it again - Ruled against the TRAVEL BAN at such a dangerous time in the history of our country," he tweeted.

Attorney General Jeff Sessions said he disagreed with the ruling.

"President Trump's executive order is well within his lawful authority to keep the nation safe."

He added: "Recent attacks confirm that the threat to our nation is immediate and real."

The dispute may end up being decided in the US Supreme Court.

Mr Trump's own tweet from 5 June was cited in the judges' ruling.

An earlier version of the travel ban, issued by Mr Trump just days after taking office, sparked confusion at airports and protests.

In the revised executive order, the 90-day ban was to apply to people from Iran, Libya, Syria, Somalia, Sudan and Yemen. It also called for a 120-day ban on all refugees, but removed references to religious minorities.

During his election campaign, Mr Trump called for a "total and complete shutdown of Muslims entering the United States".

Reacting to the latest ruling, White House spokesman Sean Spicer defended the executive order, saying: "We need every available tool at our disposal to prevent terrorists entering the United States and committing acts of bloodshed and violence."

"We continue to be confident that the president's executive order to protect this country is fully lawful and ultimately will be upheld by the Supreme Court," Mr Spicer added.