US President Donald Trump has sacked the country's acting attorney general after she took the rare step of defying the White House by refusing to enforce his sweeping immigration ban.

Sally Yates had early on Monday ordered Department of Justice lawyers to stop defending Trump's executive order, resulting in her dismissal just hours later.

"The acting attorney general, Sally Yates, has betrayed the Department of Justice by refusing to enforce a legal order designed to protect the citizens of the United States," the White House press secretary's office said in an unusually caustic statement.

"Ms Yates is an Obama Administration appointee who is weak on borders and very weak on illegal immigration."

READ MORE: What is wrong with Trump's immigration ban?

Yates had agreed to serve in an acting capacity until Senator Jeff Sessions, Trump's pick for US attorney general, was confirmed by the Senate. The White House said that Dana Boente, US attorney for the Eastern District of Virginia, would now be acting US attorney general until Sessions is approved.

Boente said in an interview with the Washington Post that he would enforce the immigration order.

Political analyst Michael Shure told Al Jazeera that the incident could prove a "stumbling block" for Sessions' confirmation, with Democrats and some Republicans now expressing opposition to the ban.

"Many people I spoke to are saying it is 'foolish'. Why didn't Trump wait, if he believed in this executive order so much, until he had his team in place? Will that affect the nominating process for the attorney general? Could it hurt his nominee? That remains to be seen," Shure said.

The decision came as Trump pressed into his second week in office, defending his sweeping immigration ban in what has become a quickly escalating political crisis

Trump's order suspends the US refugee programme for 120 days and bars all immigration for citizens of Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen for at least 90 days. The intake of refugees from Syria - ravaged by a brutal war in which some estimates say 400,000 people have been killed - has been suspended indefinitely.

Chaos at airports

Trump has argued tougher vetting of immigrants is needed to protect the US from attacks, but critics complain that his order unfairly singles out Muslims and tramples on the nation's historic reputation as a welcoming place for immigrants.

Reaction to the order was swift, with protests erupting at major airports and other major cities, including the capital - Washington, DC - as customs officials struggled to put the ban into practice.

Trump denied that his order was to blame for weekend chaos at the nation's airports, instead pointing to computer glitches, the demonstrations and even the "fake tears" of a senior opposition senator, Democrat Charles Schumer.

READ MORE: Six other times the US banned immigrants

The president publicly shifted his focus on Tuesday, signing an executive action aimed at cutting regulations for small businesses and teasing plans to unveil his Supreme Court pick.

But the immigration ban remained at the forefront of his first fortnight in the White House - and officials were reported to be pondering more actions moving forward.

According to a draft document obtained by The Associated Press news agency, Trump is now considering an executive order that would target some immigrants for deportation if they become dependent on government assistance.

The draft order calls for the identification and removal "as expeditiously as possible" of any foreigner who takes certain kinds of public welfare benefits.

Such immigrants have been barred from the US for the better part of a century and they can already be deported. But the proposed order appears to signal a Trump administration effort to actively crack down on such welfare cases.

Obama wades in

Another draft order under consideration would make changes to several of the government's foreign worker visa programs.

The White House did not immediately respond to requests for comments on the draft orders.

The furore has prompted Trump's predecessor Barack Obama to wade back into politics for the first time since leaving office and just 11 days into the new administration.

A spokesman for the former president said on Monday that Obama "fundamentally disagrees" with discrimination that targets people based on their religion. Obama spokesman Kevin Lewis alluded to, but did not specifically mention Trump's order, but added that Obama was "heartened" by the protests.

READ MORE: The lives interrupted by Donald Trump's immigration ban

The former president had said he would give Trump room to govern but that he would speak out if he believed his successor was violating basic US values.

There have been only a handful of instances in US history of top justice department officials publicly breaking with the White House.

The most famous example was in 1973, when the then-attorney general, Elliot Richardson, and his deputy resigned rather than obey President Richard Nixon's order to fire a special prosecutor investigating the Watergate scandal.

The incident, which became known as the "Saturday Night Massacre," was a public relations disaster and is seen as a turning point in Nixon's administration.