WASHINGTON — President Trump’s central campaign promise – a “big beautiful wall” along the border with Mexico – will not actually stretch across the entire border, Homeland Security Secretary John Kelly told a Senate committee Wednesday.

“It’s unlikely that we will build a wall or physical barrier from sea to shining sea,” Kelly testified to the Senate Homeland Security Committee. “I’m committed to putting it where the men and women say we should put it,” he said, referring to immigration and border enforcement agents.

Kelly’s statement was the administration’s clearest official acknowledgement that there will be no wall along the entire border, something he and other officials have suggested somewhat less directly in other forums.

Throughout the campaign, Trump had insisted that the border wall would be a physical structure, paid for by Mexico. His administration plans to request money for the wall from Congress. Trump still says he will find a way to force Mexico to reimburse the U.S. for the cost, something the Mexican government calls a non-starter.

Kelly said many aspects of the wall remain uncertain, including the cost and the structure.

“There’s no way I can give the committee an estimate of how much this will cost,” he said.

“I mean, I don’t know what it will be made of, I don’t know how high it will be, I don’t know if it’s going to have solar panels on each side, and what the one side’s going to look like, and how it’s going to be painted, have no idea.”