The Air Force One is seen at the Eleftherios Venizelos International airport before the departure of US President Barack Obama in Athens, Greece, November 16, 2016. [Photo/Agencies]

WASHINGTON -- How expensive a new version of Air Force One for future US presidents will be?

The answer, given by US President-elect Donald Trump on Tuesday, is "more than 4 billion dollars!"

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

"Cancel order!" he urged.

However, the 4-billion-dollar price tag Trump claimed for the cost of the new aircraft couldn't be immediately confirmed. So far there are no comments from both Boeing and the Pentagon.

The two 747-200 aircrafts currently used as Air Force One has been in flight since the Reagon era in 1980s. Though the two planes have been heavily modified, they are due to reach the end of their planned 30-year life in 2017.

In January, Boeing secured a contract from the Pentagon to start development work on the 747-8 jumbo jets that would replace the aging planes, according to a Wall Street Journal report.

The deal includes modifications to the aircraft, from sophisticated communications equipment to other upgrades such as antimissile devices, experts said.

The Air Force earmarked 1.65 billion dollars between 2015 and 2019 for two replacement jets, but hasn't detailed the expected cost or delivery dates for the replacement planes, said the report, adding that the Air Force had previously said it was looking to introduce the planes in 2021.

Boeing was the US government's second biggest federal contractor last year behind Lockheed Martin Corp., according to federal procurement data.