US President Donald Trump said on Friday he was sending a second aircraft carrier group to the Middle East – warning it would be a "bad day for Iran" if it fails to make a deal on its nuclear programme.

"In case we don't make a deal, we'll need it," Trump told journalists at the White House when asked about reports the USS Gerald R. Ford would be moved from the Caribbean to the Middle East.

"It'll be leaving very soon. We have one out there that just arrived. If we need it we'll have it ready, a very big force."

The US leader had already sent one aircraft carrier, the USS Abraham Lincoln, to the Middle East, as part of a fleet of 12 US Navy ships in the region. (AFP)