The White House is moving forward with plans to shift existing federal funds to pay for construction of a wall on the southern border, said a senior administration official.

In the face of several lawsuits challenging US President Donald Trump's authority to declare a national emergency to reallocate billions of dollars toward a border wall, the White House plans to first draw from the Defence Department's drug interdiction program and the Treasury Department's asset forfeiture funds before moving to divert military construction funds, the official said.