Trump vows to bring planned border wall costs 'way down'

President Donald Trump insisted early Saturday that he would bring the price of his planned Mexican border wall "way down," after US media circulated a government report estimating it would cost $21.6 billion.

US president Donald Trump Source: AAP

In the internal government study, the US Department of Homeland Security said the contentious border barrier would take more than three years to build and the price could soar much higher than the $12-15 billion figure cited by Republican House Speaker Paul Ryan last month.

"I am reading that the great border WALL will cost more than the government originally thought, but I have not gotten involved in the design or negotiations yet" Trump posted in a series of tweets. 

"When I do, just like with the F-35 FighterJet or the Air Force One Program, price will come WAY DOWN!" the president promised.

Shortly after his inauguration Trump ordered work to begin on building the wall along the 2,000-mile (3,200-kilometer) US-Mexico border -- one of his signature campaign promises -- in a bid to block migrants from illegally entering the United States.

The issue has infuriated Mexico, whose president has vowed his country will not pay for a wall, which Trump insists the country will fund.

Trump's Twitter missives came as he and his wife Melania are hosting Japanese Prime Minister Shinzo Abe and his wife Akie at the US president's Mar-a-Lago estate in Florida.

As he transitioned into the presidency prior to his swearing-in, Trump -- a real estate mogul who prides himself on his deal-making skills -- blasted what he called "out of control" costs of Lockheed Martin's F-35 stealth fighters.

WATCH: Trump welcomes Abe to White House

The company said afterwards it would trim costs for the next batch of planes, announcing $728 million in savings, although most of the price cuts were already planned ahead of Trump's involvement during a months-long contract negotiation.

The US president has also pushed for reducing the cost of the next generation Air Force One presidential jet, which is built by Boeing.

The MIT Technology Review estimated in October that the border wall bill could skyrocket to around $40 billion.

US-Mexican relations have plunged since Trump's pronouncements on the border wall, prompting Mexican President Enrique Pena Nieto to cancel a scheduled meeting with the new US leader.