US President Donald Trump's own budget proposals, to be laid out on Monday, include a request for three billion dollars as a down-payment on his Mexican border wall.
An administration official said the money would go towards purchasing private land in the Rio Grande Valley in south Texas and advance purchases of steel.
The current plan is to build some 200 kilometres of wall this year combining funding from 2018 and 19.
The border wall was a signature issue for Trump in his 2016 presidential election campaign. He pledged that Mexico would pay for the wall, which the Mexican government has insisted it will not do.