Despite the spending request, Trump told reporters when asked on Saturday that he still believes Mexico will pay for the border wall - something he repeatedly promised during his campaign. The $18 billion would expand the physical barrier on the US-Mexico border from its current 654 miles to almost 1,000 miles-about half of the total border.
In return for the cash, the Trump administration will be expected to discuss a way forward for the so-called dreamers - illegal immigrants who were brought to the United States by their parents and know no other country.
"We all want DACA to happen but we all want great security for our country", Trump said.
It also calls for 407 miles (651 kilometers) of replacement or secondary fencing, said the official, who spoke to The Associated Press on the condition of anonymity because the plan has not been made public.
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Trump is also asking for changes to the legal immigration system. The Trump administration announced in September that it was ending the Obama-era program, but gave Congress several months to act before recipients begin to lose their protected status in March. The Administration seeks that the Capitol approves 33 billion dollars to increase security measures in the mentioned area and another 15 billion in order to acquire new technologies, build roads and hire personnel.
'This is not going to get us the whole wall we need, but it's a start, ' she said. The entire border stretches nearly 2,000 miles, although much of it is already impassable.
Mexico has steadfastly rejected Trump's demand that it pay for the wall and few doubt that USA taxpayers will foot the bill if the wall is built.
The Trump administration is providing one of its most detailed blueprints yet - how the President hopes to pay for upgrades at the California-Mexico border.