By Stephanie Nebehay

GENEVA (Reuters) - U.S. President Donald Trump is "closing the door" on people fleeing Islamic State, and may try to re-open secret detention centres where torture can be used, Human Rights Watch (HRW) said on Wednesday, calling on Congress to intervene.

A temporary ban on refugees that Trump is expected to sign this week is a "particularly ugly" policy among a range of populist initiatives that could also breach the U.S. Constitution, the rights group said.

Trump looks set to "stop refugee admissions to the United States, ostensibly on security grounds," HRW head Kenneth Roth told a news briefing in Geneva.

"But in order to score a political point at home, Trump is closing the door on them. That is one particularly ugly aspect of what he is doing."

"It's as if Trump is indifferent to the extraordinary suffering that many of these refugees have been through. Many of these people are fleeing ISIS (Islamic State), or the ISIS equivalents around the world," he said.

HRW, one of the biggest international human rights groups, based in the United States, said it feared Trump would "start refilling Guantanamo" and possibly use "dark sites" on foreign soil for detainees.

"One thing we expect either today or later this week is an order from Trump to begin exploring ... the resumption of CIA dark sites," said Roth, an American.

The Washington Post published on Wednesday a draft executive order, "Detention and Interrogation of Enemy Combatants", that could open the way for terrorism suspects to be interrogated in secret prisons abroad.

"Last time, these black sites were often in democracies - they were in Poland, Latvia, Romania, if you look around the world, they were in places like Morocco, Egypt, Jordan, Thailand, Afghanistan," Roth said.

"I hope all these governments and the other prospective governments say 'no' this time around, that they don't want to be complicit in any new U.S. torture scheme."

Obama closed black sites and ordered a halt to waterboarding, a form of simulated drowning, which experts say constitutes torture banned under international law. Trump promised during his campaign to bring back waterboarding and "a hell of a lot worse".

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"If Trump is going to start toying with the Army Field Manual and weakening its preclusion of torture or other forms of inhumane and cruel interrogation, that would be very problematic," Roth said.

He called on Congress to exercise oversight over the new administration and "stand up for the Constitution and international human rights law".

"Obviously people are afraid of Trump at this stage because he does have the bully pulpit, but that's when an independent Congress standing up for principles is particularly important."

(Editing by Robin Pomeroy)