President Donald Trump said on Monday that he would be involved "indirectly" in talks between Iran and the U.S. over Tehran's nuclear program.

The talks are set to begin on Tuesday in Geneva.

The president said he was optimistic and that he believed Tehran wanted to make a deal.

"I'll be involved in those talks, indirectly. And they'll be very important," Trump told reporters aboard Air Force One.

Tensions are soaring ahead of the talks, with the U.S. deploying a second aircraft carrier to the Middle East.

The U.S. military is preparing for the possibility of a sustained military campaign if the talks do not succeed, U.S. officials have told Reuters.

Asked about the prospects for a deal, Trump said Iran sought tough negotiations but learned the consequences of such a hardened stance last summer when the U.S. bombed Iranian nuclear sites.

Trump suggested Iranians were motivated this time to negotiate.

"I don't think they want the consequences of not making a deal," Trump said.

Prior to the U.S. joining Israel in striking Iranian nuclear sites in June, Iran-U.S. nuclear talks had stalled over Washington's demand that Tehran forgo enrichment on its soil, which the U.S. views as a pathway to an Iranian nuclear weapon.

Iran's civil defense organization on Monday held a chemical defense drill in the Pars Special Economic Energy Zone to strengthen preparedness for potential chemical incidents in the energy hub located in southern Iran.