US President Donald Trump has indicated he will decide on whether to attack Iran in the next 10 to 15 days.
Speaking at the inaugural "Board of Peace" meeting in Washington DC, Mr Trump said "bad things" would happen if a "meaningful deal" was not reached in ongoing nuclear talks.
After saying the US had "totally decimated" Iran's nuclear program when it bombed three sites in June, Mr Trump said: "Now we may have to take it a step further, or we may not."
"Maybe we're going to make a deal," he said.
"You're going to be finding out over the next, probably, 10 days."
Asked later if he was giving Iran a deadline, Mr Trump said: "I think that would be enough time — 10, 15 days, pretty much maximum."
But an attack could come much sooner: last year, Mr Trump said he would make a decision on Iran "within the next two weeks", then ordered strikes on Iran two days later.
The US has deployed aircraft carriers, warships and other military assets to the region in recent weeks, and American media reports suggest an attack could be imminent.
CNN reported the US military was prepared to strike "as early as this weekend", but officials told the network Mr Trump had not made a decision.
American representatives have also held indirect negotiations with Iran, pressuring the ruling Islamic regime to curb its nuclear enrichment program.
The most recent talks, earlier this week, were brokered by Omani mediators in Geneva, Switzerland.
Mr Trump said special envoy Steve Witkoff and his son-in-law, Jared Kushner, had developed a "good relationship" with Iranian representatives during the negotiations.
"Good talks are being had," he said.
"It's proven to be, over the years, not easy to make a meaningful deal with them.
"And we have to make a meaningful deal. Otherwise bad things happen."
Preparing for conflict
Earlier this week, Iran said it temporarily closed the Strait of Hormuz — a shipping route used to transport 20 per cent of the world's oil — in what was widely seen as a warning to the US.
Iran said it closed the strait for live fire drills.
Iranian Foreign Minister Abbas Araqchi later said Iran and the US had "been able to reach a general agreement on some guiding principles" during the Geneva talks.
Multiple US media outlets have reported Mr Trump is considering a lengthy military campaign rather than a quick operation like last year's "Midnight Hammer" strikes on nuclear sites.
The Reuters news agency, citing two anonymous officials, reported the US military was preparing for the possibility of sustained, weeks-long operations if Mr Trump orders an attack.
Satellite imagery appears to show Iran preparing for an attack, according to analysts.
Tunnels leading to a nuclear facility have been buried with soil, and parts of the mysterious "Pickaxe Mountain" complex appear to have been reinforced.
Iran has argued its nuclear program is for peaceful purposes, even though it has enriched uranium well beyond purity levels required for energy generation.
Iran's Supreme Leader, Ayatollah Ali Khamenei, has warned that a US attack would spark a "regional war" in the Middle East.
