US President Joe Biden warned on Thursday that his administration was preparing "additional measures" against Iran as concerns grow that talks on halting Tehran's nuclear program are set for failure.
"The president has asked his team to be prepared in the event that diplomacy fails, and we must turn to other options," White House Press Secretary Jen Psaki said.
The troubled negotiations with Iran have resumed in Vienna.
"We will have no choice but to take additional measures," she added.
Meanwhile, at the Pentagon, US Defense Secretary Lloyd Austin met with Israeli counterpart Benny Gantz, and both sides said they would expand cooperation in the face of the Iranian "threat."
"I'm deeply concerned about the Iranian government's nuclear actions in recent months, both its continued provocations and its lack of constructive diplomatic engagement," said Austin.
The International parties to the 2015 nuclear deal restarted the talks with Iran on its nuclear programme Thursday for what the chair of the negotiations called a "difficult endeavour" to revive the deal between Iran and world powers.