"We have a tremendous military force on the southern border, we have large numbers of people trying to get into our country," he told reporters at the White House ahead of a visit to California.

"They built great fencing, they built a very powerful fence," he added.

Some 5,900 active-duty troops are now stationed along the border, a contentious deployment in support of civilian forces that Trump ordered ahead of the recent midterm elections.

Opponents have criticized the cost and usefulness of the operation, dismissing it as a political stunt.

An additional 2,100 or so National Guardsmen have been deployed to support operations at the border, bringing the total military presence to about 8,000.