"I am establishing new vetting measures to keep radical Islamic terrorists out of the United States of America. We don't want them here," Trump said after signing an executive order at the Pentagon.
The executive order "Protection of The Nation From Foreign Terrorist Entry Into The United States" notes that the steps taken by the US in the aftermath of 9/11 has not been able to deter terrorists from entering the country.
The countries impacted are Iran, Iraq, Syria, Sudan, Libya, Yemen and Somalia, according to a White House official.
The controversial move, signed a week after he was sworn- in as the President, fulfills the vow Trump made on the campaign trail to limit Muslim immigration to the US.
"We want to ensure that we are not admitting into our country the very threats our soldiers are fighting overseas. We only want to admit those into our country who will support our country and love deeply our people," Trump said.
Deteriorating conditions in certain countries due to war, strife, disaster, and civil unrest increase the likelihood that terrorists will use any means possible to enter the US, the executive order said.
The US must be vigilant during the visa-issuance process to ensure that those approved for admission do not intend to harm Americans and that they have no ties to terrorism, it said.
In addition, the US should not admit those who engage in acts of bigotry or hatred (including "honour" killings, other forms of violence against women, or the persecution of those who practice religions different from their own) or those who would oppress Americans of any race, gender, or sexual orientation, it said.
Saudi Arabia, it would resort to extreme vetting.
As per the executive order, the list of such countries could be expanded if they fail to provide information to the US about their citizens applying for a US visa.
In an interview to Christian Broadcast Network, Trump said he would give priority to Christian refugees. "We are going to help them," he said.
"They've been horribly treated. Do you know if you were a Christian in Syria it was impossible, at least very tough, to get into the United States?," he said.
"If you were a Muslim you could come in, but if you were a Christian, it was almost impossible and the reason that was so unfair, everybody was persecuted in all fairness, but they were chopping off the heads of everybody but more so the Christians. And I thought it was very, very unfair," Trump said.
Democratic Senator Kamala Harris wrote that the order had been signed on Holocaust Memorial Day. "Make no mistake - this is a Muslim ban," she wrote.
"During the Holocaust, we failed to let refugees like Anne Frank into our country. We can't let history repeat itself," she said.'
Malala Yousafzai, the teenage Nobel Peace Laureate who was once shot by the Taliban following her advocacy for women's education in Pakistan, wrote that she was "heartbroken".
Facebook founder Mark Zuckerburg also posted a lengthy note to his own profile on the site, saying he was "concerned" about the president's executive orders, and noting that he, like many Americans, is the descendant of immigrants.
