Former US president Barack Obama expressed his objections Monday to any faith-based discrimination, in an apparent dig at his successor Donald Trump's ban on nationals of seven Muslim-majority countries entering the country.

"With regard to comparisons to president Obama's foreign policy decisions, as we've heard before, the president fundamentally disagrees with the notion of discriminating against individuals because of their faith or religion," his spokesman Kevin Lewis said in a statement.

The statement -- Obama's first on politics since leaving the White House on January 20 -- came amid an uproar over Trump's order on Friday to tighten controls on immigrants from the seven countries and to temporarily halt all resettlement of refugees.

The former president is "heartened" by protests that have taken place across the country, Lewis said.

"Citizens exercising their constitutional right to assemble, organize and have their voices heard by their elected officials is exactly what we expect to see when American values are at stake," the statement added.

The statement came after the White House defended its policy, which saw more than 100 travelers detained at US airports and hundreds more blocked abroad, as essentially the same as previous rules implemented during Obama's presidency.

Former Obama national security spokesman Ben Rhodes said in a series of tweets that the tight vetting of Iraqi refugees in 2011 was not the same as an executive order (EO) like Trump's banning immigrants from Iraq.

"There was no ban on Iraqis in 2011. Anyone pushing that line is hiding behind a lie because they can't defend the EO," Rhodes said.

"More inter-agency vetting of Iraqi refugees in response to threat is standard process. EO banning people from several countries is not."

Former presidents traditionally do not weigh in publicly on a current president's statements or policies. Before Obama left office, he said any effort to enforce systematic discrimination, erode voting rights, muzzle the press or round up young immigrants, would cause him to speak out.