Last week, Trump pulled back from a threat to strike Iran over its deadly crackdown on anti-government protests after the White House said Tehran had halted planned executions of demonstrators.

But the Republican president on Thursday confirmed continuing military preparations. US media have reported in the past week that the USS Abraham Lincoln carrier strike group was ordered from maneuvers in the South China Sea to the Middle East.

"We're watching Iran," Trump told reporters on Air Force One as he flew back from the World Economic Forum in Davos, Switzerland.

"You know we have a lot of ships going that direction, just in case... We have a big force going toward Iran," the president said.

"I'd rather not see anything happen but we're watching them very closely."

He described the force as "an armada" and "massive fleet," but added, "maybe we won't have to use it."

Trump reiterated that his threat to use force against Tehran had stopped 837 hangings of protesters. He also confirmed he was open to talking with Iran.

Iranian authorities on Wednesday gave their first official toll from the protests -- which appear to have ebbed in recent days -- saying 3,117 people were killed. Rights groups say the actual number of dead could be far higher.

Trump has repeatedly left open the option of new military action against Iran after Washington backed and joined Israel's 12-day war in June aimed at degrading the Islamic republic's nuclear and ballistic missile programs.