US President Donald Trump has said it is the “calm before the storm” as he met military leaders, without giving further details.
The cryptic comments came hours after reports he was planning to withhold support for the Iran nuclear deal.
But the “storm” could also refer to heightened tensions with North Korea.
He had earlier told his top defence officials he expected them to provide “a broad range of military options… at a much faster pace” in future.
Mr Trump, posing with his wife Melania, as well as military leaders and their wives ahead of a White House dinner following Thursday’s meetings, asked the waiting press if they knew “what this represents”.
“Maybe it’s the calm before the storm,” he said.
But when the waiting journalists pressed him on what storm he was referring to, he would only say: “You’ll find out.”
The Trump administration’s sights appear to be set on two countries in particular currently: North Korea and Iran. Both involve nuclear programmes, and both were touched on during Thursday’s talks with US military leaders.
Mr Trump accused Iran of having “not lived up to the spirit of the agreement” brokered with Iran under his predecessor, Barack Obama.
The 2015 accord was designed to prevent Iran developing a nuclear weapon, with the president’s administration having to certify to Congress that Iran is upholding its part of the deal every 90 days.
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Mr Trump has previously described the deal signed by Iran, the US, the UK, France, China, Russia and Germany as “one of the worst deals I’ve seen”.
US media say the president will announce next Thursday that he would not be certifying the deal on the grounds it does not serve US security interests.
This would leave Congress sixty days to decide whether to re-impose sanctions on Iran.
But some of his top advisers, such as Defence Secretary James Mattis, appear to back the deal.
Speaking in the White House’s Cabinet Room, President Trump said: “The Iranian regime supports terrorism and exports violence and chaos across the Middle East.”
“That is why we must put an end to Iran’s continued aggression and nuclear ambitions. You will be hearing about Iran very shortly.”
However, Mr Trump’s “storm” could also refer to North Korea, which the US wants to halt its weapons programme.
Mr Trump has engaged in a war of words with the country’s leader, Kim Jong-un, in recent months, threatening to “totally destroy” North Korea during a speech at the UN General Assembly in September.
The US wants Pyongyang to halt its weapons programme, which has seen it perform repeated missile tests, as well as claim to have successfully tested a miniaturised hydrogen bomb which could be loaded on to a long-range missile.
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On Thursday, Mr Trump’s words were more measured.
“In North Korea, our goal is denuclearisation,” he said. “We cannot allow this dictatorship to threaten our nation or our allies with unimaginable loss of life.”
“We will do what we must do to prevent that from happening. And it will be done, if necessary, believe me.”
Trump: This is the calm before the storm