The commander of Iran's Revolutionary Guards warned Washington Thursday that the force had its "finger on the trigger" in the wake of mass protests, as US President Donald Trump said Tehran still appeared interested in talks.

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 Iranian nuclear and ballistic missile programmes.

Trump said Thursday a US naval "armada" was heading toward the Gulf, adding: "We're watching Iran."

A fortnight of protests starting in late December shook Iran's clerical leadership under supreme leader Ayatollah Ali Khamenei, but the movement has petered out in the face of a crackdown that activists say killed thousands, accompanied by an unprecedented internet blackout.

The prospect of immediate American action against Tehran appears to have receded, with both sides insisting on giving diplomacy a chance.

On his way back from the World Economic Forum in Davos, Trump told reporters on Air Force One the United States was sending a "massive fleet" toward Iran "just in case."