President Donald Trump told reporters aboard the Air Force One that the conditions are not in place for a thorough overhaul of the US immigration system.

"What I'd like to do is a comprehensive immigration plan. But our country and political forces are not ready yet … There are two sides of a story. It's always tough," he said in what was originally supposed to be an off-the-record session with journalists accompanying him on a visit to France.

The White House subsequently authorised media outlets to report the President's comments later on Thursday, reports Efe news.

His statement on immigration reform came in response to a question about the future of the Deferred Action for Childhood Arrivals (DACA) programme, established by predecessor Barack Obama to shield hundreds of thousands of undocumented youths from deportation.

Trump said he has not made a decision over the DACA, while emphasising that he – and not his subordinates – who would make the final determination.

"It's a decision that I make and it's a decision that's very very hard to make. I really understand the situation now," he said.

Last month, the Department of Homeland Security said that DACA would remain in effect for the time being, though Texas and a number of other states have threatened to sue the federal government if the program is not ended by September 5.

On the related matter of his plan for a wall on the US-Mexican border, Trump said that his remarks about installing solar panels on the structure had not been in jest.

"We have major companies looking at that. Look, there's no better place for solar than the Mexico border – the southern border. And there is a very good chance we can do a solar wall, which would actually look good," he said.

The President said the wall needs to be transparent for the safety of people on the US side.

"And I'll give you an example. As horrible as it sounds, when they throw the large sacks of drugs over, and if you have people on the other side of the wall, you don't see them – they hit you on the head with 60 pounds of stuff? It's over. As crazy as that sounds, you need transparency through that wall," Trump said.

He also suggested that the barrier would not have to extend the entire length of the 2,000-mile border.

"Remember this, it's a 2,000 mile border, but you don't need 2,000 miles of wall because you have a lot of natural barriers. You have mountains. You have some rivers that are violent and vicious. You have some areas that are so far away that you don't really have people crossing. So you don't need that. But you'll need anywhere from 700 to 900 miles," he added.