BEFORE leaving office, Barack Obama warned he was willing to be vocal in retirement.

Well, the former US president has already taken his first subtle swipe at Donald Trump. Today Mr Obama released a statement that was clearly alluding to Mr Trump's controversial immigration ban on citizens from seven Muslim-majority countries.

"President Obama is heartened by the level of engagement taking place in communities around the country. Citizens exercising their Constitutional right to assemble, organise and have their voices heard by their elected officials is exactly what we expect to see when American values are at stake," spokesman Kevin Lewis said on Mr Obama's behalf.

"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 and religion."

Mr Trump has rejected accusations his executive order amounts to a "Muslim ban", pointing out that it doesn't include dozens of majority-Muslim countries. Instead, he says it is aimed at stopping extremists from entering the United States.

The order, signed on Friday, bars the citizens of seven nations - Iraq, Iran, Syria, Sudan, Somalia, Libya and Yemen - from travelling to the US for at least 90 days. Mr Trump has also imposed a 120-day suspension on America's refugee program.