Trump says Iran regime change best, 'fear' is powerful motivator

US President Donald Trump said Friday that a change of government in Iran would be the "best thing that could happen," as he sent a second aircraft carrier to the Middle East to ratchet up military pressure on the Islamic Republic.

Trump's comments were his most overt call yet for the toppling of Iran's clerical establishment, and came as he pushes on Washington's arch-foe Tehran to make a deal to limit its nuclear programme.

At the same time, the exiled son of the Iranian shah, toppled in the 1979 Iranian revolution, renewed his calls for international intervention following a bloody crackdown on protests by Tehran.

"Seems like that would be the best thing that could happen," Trump told reporters at the Fort Bragg military base in North Carolina when a journalist asked if he wanted "regime change" in Iran.

Trump declined to say who he would want to take over in Iran from Supreme Leader Ayatollah Ali Khamenei, but he added that "there are people."

He has previously backed off full-throated calls for a change of government in Iran, warning that it could cause chaos, although he has made threats towards Khamenei in the past.

Speaking earlier at the White House, Trump said that the USS Gerald R. Ford, the world's largest warship, would be "leaving very soon" for the Middle East to up the pressure on Iran.

"In case we don't make a deal, we'll need it," Trump said.

The giant vessel is currently in the Caribbean following the US overthrow of Venezuela's Nicolas Maduro. Another carrier, the USS Abraham Lincoln, is one of 12 US ships already in the Middle East.

'Fear' is powerful motivator

Trump told US troops on Friday that Iran has been "difficult" in nuclear negotiations and suggested that instilling fear in Tehran may be necessary to resolve the standoff peacefully.

"They've been difficult to make a deal," Trump said of the Iranians before an audience of active-duty soldiers at Fort Bragg Army base in North Carolina, after US officials said they were sending a second aircraft carrier to the Middle East.

"Sometimes you have to have fear. That's the only thing that really will get the situation taken care of."

During his address, Trump also referenced the US bombing of Iran's nuclear sites last June.

Earlier, he said the deployment of the world's largest aircraft carrier was being made so "we'll have it ready" should negotiations with Iran fail.

Oman facilitated talks between Iran and the US last week, which a spokesperson for Iran's foreign ministry said had allowed Tehran to gauge Washington's seriousness and showed enough consensus for diplomacy to continue. The date and venue of the next round of US-Iran talks have yet to be announced.

The head of the UN nuclear watchdog, Rafael Grossi, said Friday that reaching an accord with Iran on inspections of its processing facilities was possible but "terribly difficult".