Former President Barack Obama weighs in on Donald Trump's presidency for the first time.

Former US President Barack Obama has issued his first official statement since leaving the Oval Office nine days ago, to respond to President Donald Trump’s temporary travel ban on people from several Muslim-majority countries.

Obama said he “fundamentally disagrees with the notion of discriminating against individuals because of their faith and religion.”

“President Obama is heartened by the level of engagement taking place in communities around the country,” spokesman Kevin Lewis said on his behalf.

“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.

"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."

In a statement released yesterday, President Trump said the executive order, which bars citizens of seven nations from travelling to the US for at least 90 days, was "not about religion".

"This is about terror and keeping our country safe. There are over 40 different countries worldwide that are majority Muslim that are not affected by this order," he said in a statement issued Sunday evening, US time.

Obama's statement comes as a 15-year-old schoolboy from Melbourne claims to be the first Australian affected by Trump's travel ban.

Pouya Ghadirian, who was born and raised in Melbourne and holds dual Iranian-Australian citizenship, was refused a non-immigrant tourist visa at the US Consulate office in Melbourne.

He had been planning on travelling to the United States as part of a school trip, where he would visit Orlando, Washington and the US Space and Rocket Centre.

“They were a bit shocked and they didn’t know how to handle it. They said they had terrible news,” Ghadirian told AAP.

“They said it was the first time it had happened in an Australian embassy. I was really and upset when I found out that I couldn’t go and had been looking forward to it for around a year."