Claim: Much of the wall has already been fully renovated or built. Mexico is paying for the wall through the new US-Mexico-Canada trade agreement.
Verdict: The border authorities say work has begun on building improved border security infrastructure. The money made available so far is largely tied to barrier designs that already exist. The trade agreement with Mexico and Canada is not yet in place and it's not clear how this would directly lead to revenue from Mexico to pay for the wall.
US President Donald Trump wants to spend billions of dollars building a wall along the US-Mexico border.
He needs the US Congress to approve the funding for his plan but he has come up against strong opposition, and the Democratic party doesn't want to stump up the money.
However, Mr Trump says there has already been significant progress.
Writing on Twitter he says "much of the wall has already been fully renovated or built. We have done a lot of work."
So, just how much has been built so far - and is Mexico paying?
Building a wall along the border with Mexico was one of Mr Trump's key election promises.
The White House says the wall is critical to stopping illegal immigrants and drugs entering the country.
The border is 1,954 miles (3,145 km) long, with about 650 miles of various types of fencing already in place through California, Arizona, New Mexico and Texas.
According to documents obtained by CNN at the beginning of 2018, officials told Congress that the Trump plan would mean 864 miles of new wall and 1,163 miles of replacement wall. It would cost $33bn (£26bn).
Why is President Trump talking about the wall now?
The current row between the president and Congress is over a spending package of more than $5bn (£3.9bn) for the wall.
But Democratic lawmakers in the House of Representatives have so far refused to agree to any additional funding for the wall. They have offered $1.3bn for border security, such as improved surveillance and fencing, but not the wall.
This funding for border security is part of a larger budget that Congress is trying to pass. The impasse has led to a partial government shutdown that began on 22 December.
Mr Trump has said he will not sign a bill to reopen government that doesn't include money for the wall.
At the end of last year the lower house, then controlled by Republicans, passed a bill that met the president's request, but it failed to get enough votes in the Senate.