President Donald Trump on Monday said he is sticking to his pledge to make Mexico pay for his proposed border wall "one way or the other" — despite his request for federal funding for the structure and threat to shut down the government over the money.

"We need the wall. It's imperative," Trump said at a joint press conference with Finnish President Sauli Niinisto on Monday. "We may fund it through the United States but ultimately Mexico will pay for the wall."

The president did not specify how he would compel Mexico to pay for the project, but said it "may be through reimbursement."

As a candidate, Trump pushed for a physical barrier across the entire U.S.-Mexico border. He argued that the structure would curb illegal immigration and the flow of drugs into the U.S.

Mexico's government has repeatedly said it will not fund the wall, and the Trump administration has gone to Congress for funding. Facing a Sept. 30 deadline to fund the government and keep it open, congressional Democrats have said they will not vote for a measure that includes border wall money.

Earlier this month, Trump said he will build the wall "if we have to close down our government."

Trump on Monday claimed the barrier "will stop much of the drugs pouring into this country and poisoning our youth."

He added that he hopes a shutdown is "not necessary."

When asked about the wall, Trump also launched into a tirade against the North American Free Trade Agreement, saying Mexico has been "very difficult" as the U.S. aims to renegotiate the three-nation trade deal.

Renegotiation of NAFTA started recently among the three countries. On Monday, Trump again said the U.S. may need to at least start the process of terminating NAFTA before it can reach a desirable deal.