Media playback is unsupported on your device Media caption Trump responds to his own Boeing Tweet

US President-elect Donald Trump has said he wants to cut government costs by cancelling the order for new planes to carry the American president.

Mr Trump tweeted: "Boeing is building a brand new 747 Air Force One for future presidents, but costs are out of control, more than $4 billion. Cancel order!"

The government has a contract with Boeing to build two or more new planes.

The White House appeared to cast doubt on the figures quoted by Mr Trump.

"Some of the statistics that have been cited, shall we say, don't appear to reflect the nature of the financial arrangement between Boeing and the Department of Defence," White House spokesman Josh Earnest said.

The new planes would enter service around 2024.

Boeing shares fell more than 1% after the president-elect's tweet, but recovered most of their losses in afternoon trading.

Mr Trump would not fly on the new planes unless he won a second term in the 2020 election.

Media playback is unsupported on your device Media caption Megyn Kelly: Being a 'woman of power' fuelled Trump backlash

The president-elect also announced on Tuesday that Japan's SoftBank has agreed to invest $50bn (£39.4bn) in the US aimed at creating 50,000 new jobs.

Mr Trump revealed the plan after meeting SoftBank CEO Masayoshi Son at Trump Tower.

"Masa said he would never do this had we (Trump) not won the election!" he tweeted.

In other developments:

In his last major speech on national security, President Obama warned the US should not lose sight of it founding values while fighting terrorism

Mr Trump sold his entire share portfolio in June, his spokesman says, in a move that could address conflict-of-interest concerns

Congressional Republicans warned Mr Trump they would block his plan to impose punitive tariffs on US companies that relocate abroad

A Republican elector in Texas vowed to withdraw his backing of Mr Trump when the electoral college meets next week

Vice-President Joe Biden, 74, suggested he would be open to running for president for a third time, in 2020

'Could cost more' - Zoe Thomas, BBC New York business correspondent

As president and commander-in-chief, Donald Trump will have the power to cancel the contract with Boeing for the new planes.

But if he does, it could cost the US taxpayer even more as the new president tries to save money. The US government has already signed a contract with Boeing for $170m (£134m; €158m). Additional funding has also been earmarked for the two new planes.

The Government Accountability Office - an independent government auditor - estimates the final cost will be $3.2bn. The planes are still in early design phases, though - much of the money has yet to be spent and has not had a chance to overrun the cost estimates.

Negotiation between Boeing and the US government could cut some of the costs, but if Mr Trump pulls out of the Boeing contract entirely the country may lose the money it is already contracted to pay.

Mr Trump now uses his own plane, but as president he would travel aboard Air Force One, which is equipped with special safety, defensive and communications equipment.

He is known for his admiration of his Trump-branded Boeing 757 jet, boasting to Rolling Stone last year that his aircraft was "bigger than Air Force One, which is a step down from this in every way".

Media playback is unsupported on your device Media caption The BBC asked aviation expert Chris Yates to describe what facilities Air Force One has on board.

"Did you know it was featured on the Discovery Channel as the world's most luxurious jetliner?" he said at the time.

The president-elect told reporters on Tuesday at Trump Tower in New York that Boeing was "doing a little bit of a number" and the cost was "ridiculous".

"We want Boeing to make a lot of money, but not that much money," he added.

Image copyright Reuters

A flying Oval Office

Technically, "Air Force One" is a call sign for any aircraft carrying the US president. However the term is mostly used to refer to two customised Boeing 747-200B jets

Capable of in-flight refuelling, and equipped with secure communications equipment, they have been described as "flying Oval Offices"

Inside, the president and his travel companions enjoy 4,000 sq feet (400 sq m) of floor space on three levels

This includes a presidential suite as well as quarters for advisers, Secret Service officers, and the travelling press corps

A medical suite can function as an operating room, and a doctor is always on board

The plane's two food preparation galleys can feed 100 people at a time.

Mr Trump's remarks came after the Chicago Tribune published a column early on Tuesday in which Boeing chief executive Dennis Muilenburg suggested the president-elect roll back his anti-trade rhetoric.

"If we do not lead when it comes to writing these [trade] rules, our competitors will write them for us," Mr Muilenburg told the newspaper.

The Government Accountability Office estimates that the project's overall cost will be $3.2bn, a figure that is expected to rise.

The US Air Force said it had budgeted $2.7bn for the project, "but expects this number to change".

Boeing spokesman Todd Blecher, in a statement, said: "We are currently under contract for $170m to help determine the capabilities of these complex military aircraft that serve the unique requirements of the president of the United States.

"We look forward to working with the US Air Force on subsequent phases of the programme, allowing us to deliver the best planes for the president at the best value for the American taxpayer."