US President Donald Trump signs an executive order imposing the sanctions on Monday, after Tehran's downing of an American drone last week.
US president signed an executive order, which will lock billions of dollars more in Iranian assets.
Reports state Pentagon attempting to disable Iran's rocket launch systems.
But Tehran warns of growing risk of military confrontation with US.
MAS flights to London and Middle East among those affected after Iran shoots down US drone.
An Iranian official says any attack will have international and regional consequences.
It is unknown if the US president changed his mind or his administration was worried about logistics or strategy.
The incident followed an earlier attempt to shoot down a US military drone last week.
President says last week’s tanker attacks in the Gulf of Oman only had a 'very minor' impact.
Acting US Defence Secretary Patrick Shanahan announces deployment of about 1,000 more troops for 'defensive purposes'.
Mohammed bin Salman also joins chorus blaming Tehran for the attacks on two oil tankers.
'Negotiation has no benefit and carries harm,' says Ayatollah Ali Khamenei.
Foreign Minister Javad Zarif adds no one should be under the illusion it can confront Iran in the region.
It claims two armed drones struck oil pumping stations in a 'cowardly' act of terrorism.