Donald Trump at a campaign event in Iowa. REUTERS/Carlo Allegri Donald Trump on Tuesday appeared to reiterate his support for a physical wall along the US-Mexico border after days of speculation about whether he would support his previous immigration policies.

In a tweet Tuesday morning, the Republican presidential nominee reaffirmed his support for a wall and teased a speech on immigration he's set to deliver on Wednesday.

"From day one I said that I was going to build a great wall on the SOUTHERN BORDER, and much more. Stop illegal immigration. Watch Wednesday!" Trump wrote.

Though immigration has been a major theme of his campaign, in recent weeks the real-estate magnate and his campaign have waffled on some of the central premises of Trump's immigration pitch to Republican primary voters. The campaign has sent mixed signals about whether Trump still supports creating a deportation force to forcibly remove over 10 million immigrants living in the US without permission.

Some campaign surrogates have seemed to back away from the promise to build a wall along the Southern border. Former New York City Mayor Rudy Giuliani suggested in an interview this week that some of the wall would have digital features; last month, former Texas Gov. Rick Perry promised a similar virtual wall.

But in an interview on "Fox and Friends" on Tuesday, Trump spokesman Jason Miller reaffirmed that the wall would be physical.

"There's going to be a physical wall," Miller said. "There will be a physical wall on the Mexico border, and, as we know, Mexico is going to pay for it."