Department of Homeland Security Secretary Kirstjen Nielsen told lawmakers Tuesday that is is “not aware” of any deal with Mexico to build a wall along its northern border with the United States.

“Do you know whether we have arrangements with Mexico to pay for it?” Sen. Dick Durbin asked during a Senate Judiciary Committee hearing Tuesday.

Nielsen replied: “I know that we have arrangements with Mexico to secure our border,” to which Durbin, an Illinois Democrat, responded: “What arrangements do we have with Mexico to pay for the wall as President Trump promised the American people?”

Trump consistently promised a wall along the U.S.-Mexico border during the 2016 presidential campaign, most recently tweeting Tuesday morning: “We must have Security at our VERY DANGEROUS SOUTHERN BORDER, and we must have a great WALL to help protect us, and to help stop the massive inflow of drugs pouring into our country!”

“I am not aware. I don’t know what you mean by arrangement. We have a lot of agreements with them to increase border security,” Nielsen explained.

When pushed again by Durbin if any of the agreements are for Mexico to pay for it, Nielsen declined to either confirm nor deny.

“Are they paying for the wall?” he asked.

“My priority is to increase border security and to build that wall that will work,” Nielsen she said.

Tension is high in Washington as immigration policy agreements threaten to lead to a government shutdown on Friday. While Trump and congressional Republicans demand money for the border wall as part of an immigration deal, Democrats say they won’t vote to fund the government past Friday if there is no deal on the Deferred Action on Childhood Arrivals program.

"The Democrats want to shut down the Government over Amnesty for all and Border Security. The biggest loser will be our rapidly rebuilding Military, at a time we need it more than ever," Trump wrote in another Tuesday tweet. "We need a merit based system of immigration, and we need it now! No more dangerous Lottery."