Donald Trump has signed a revised travel ban that will temporarily halt entry to the US for people from six Muslim-majority nations.

Under the Republican president's order announced on Monday, a 90-day ban on travel to the US will be imposed on citizens of Iran, Libya, Syria, Somalia, Sudan and Yemen.

Travellers holding pre-existing visas would still be allowed entry, according to the new order, which will come into effect at midnight on March 16.

"Green card" holders - that is, those who have US permanent residence - will not be affected by the order.

Al Jazeera's Alan Fisher, reporting from Washington, DC, said: "[US officials] have tried to take what was the existing executive order, make it much tighter, and essentially make it bulletproof in the courts."

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In initial reactions, rights groups criticised the new order, with the American Civil Liberties Union (ACLU) saying that the new ban was a "scaled-back version that shares the same fatal flaws".

In a statement, ACLU said: "The only way to actually fix the Muslim ban is not to have a Muslim ban. Instead, President Trump has recommitted himself to religious discrimination and he can expect continued disapproval from both the courts and the people."

Unlike the previous ban, the new directive does not include Iraq in its list of countries targeted, following pressure from the Pentagon and state department which had urged the White House to reconsider given Iraq's key role in fighting the Islamic State of Iraq and the Levant (ISIL) group.

The new version also removed language that would give priority to religious minorities.

Critics had accused the administration of adding such language to help Christians get into the US while excluding Muslims.

'Positive message' for Iraq

The Iraqi government said the revised order sends a "positive message" about the future of bilateral relations as the two countries work to combat ISIL, also known as ISIS.

Saad al-Hadithi, government spokesman, said the decision to revise the ban shows that there is a "real partnership" between Washington and Baghdad.

Rex Tillerson, US secretary of state, said that the renewed ban is "a vital measure for strengthening our national security".

"With this order, President Trump is exercising his rightful authority to keep our people safe," he said.

Attorney General Jeff Sessions said the order "responsibly provides a needed pause so we can carefully review how we scrutinise people coming here from these countries of concern".

"Three of these nations are state sponsors of terrorism," Sessions said, referring to Iran, Sudan and Syria, adding that others had served as "safe havens" for fighters.

Trump's first order, signed on January 27, led to chaos at airports, protests and international condemnation.

That order resulted in more than two dozen legal cases in US courts and was ultimately blocked by the courts.

Many said the order partially fulfilled Trump's campaign promise to ban Muslims from entering the US.

Bob Ferguson, the attorney general of Washington state, which succeeded in having the previous ban suspended, said he was "carefully reviewing" the new order.

"There's going to be a very orderly process," a senior official from the homeland security department said.

"You should not see any chaos, so to speak, or alleged chaos at airports. There aren't going to be folks stopped tonight from coming into the country because of this executive order."

'Unconstitutional actions'

Senator Ted Cruz praised the new order, which he described as a "responsible step of acting to prevent terrorists from infiltrating our refugee programmes".

"In contrast to the hysteria and mistruths that are still being pushed by the media, President Trump’s executive order implements a four-month pause in refugee admissions so that stronger vetting procedures can be put in place," Cruz said.

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Peter Roff of Frontiers for Freedom, a right-wing think-tank, also welcomed the revised immigration order.

"Muslims are not banned from America," he told Al Jazeera.

"On the contrary, Muslims are welcomed in America, but we are only trying to prevent terrorists from coming in who might be infiltrating our country as refugees.

"ISIS and al-Qaeda terrorists killed more Muslims than Christians and Jews."

By contrast, leading Democrats condemned the new ban, with the party's new leader saying "we have a responsibility to fight back".

Chuck Schumer, leader of the minority Democrats in the Senate, said he expected the revised order to have the same uphill battle in the courts as the original version.

"A watered-down ban is still a ban," he said in a statement.

"Despite the administration's changes, this dangerous executive order makes us less safe, not more. It is mean-spirited and un-American. It must be repealed."

Tom Perez, chair of the Democratic National Committee, said party members have a "responsibility to fight back".

"I've seen firsthand the difference we can make when we refuse to accept the hateful, immoral, unconstitutional actions of the Trump administration," Perez said.

Senator Dianne Feinstein said the ban "does not strengthen our national security".

"Painting more than 150 million people with the same broad brush is contrary to the principle of religious freedom and will do nothing to make us safer," she said.