In a statement, Bolton said: “I spoke to the President over the last several days, and President Trump told me that if Iran does anything at all to the negative, they will pay a price like few countries have ever paid before."
Sunday night, Trump fired off a tweet in response to what he called a threat made by Iranian President Hassan Rouhani. The president's response triggered new concerns that the already-tense situation could escalate into a potential military conflict.
Trump withdrew the U.S. from an Obama-era deal designed to discourage Iran's nuclear ambitions. In renouncing the 2015 agreement, the U.S. is reinstating harsh sanctions on Iran, which is the fifth-biggest oil producer in the world, and is expecting most buyers to halt their purchases of Iranian crude oil by November.
Bolton's statement comes after a week of walkbacks by the Trump administration following the president's summit with Russian President Vladimir Putin and Trump's comments on the Federal Reserve's interest rate policy.
Trump eventually said he supported the intelligence community's findings that Russia interfered with the U.S. election in 2016, after he had suggested that he accepted Putin's denials during their Helsinki press conference. Later in the week, the White House said Trump respected the Fed's independence after he complained that the central bank's planned interest rate increases threaten progress in the economy.
This time, though, the White House is sticking with the president's harsh rhetoric through Bolton, a foreign-policy hardliner and an Iran hawk.
Bolton is responsible for advising Trump on a wide spectrum of national security issues, from the U.S.-led coalition against the Islamic State to China's aggressive actions in the South China Sea to North Korea's growing nuclear threat.
As George W. Bush's undersecretary of state for arms control, Bolton was a supporter of the invasion of Iraq and was confident that Iraqi president Saddam Hussein possessed weapons of mass destruction.
After leaving the Bush administration, Bolton joined the American Enterprise Institute, a conservative think tank, where he expressed some of his confrontational rhetoric in op-eds such as, "To Stop Iran's Bomb, Bomb Iran."
Bolton was also a vocal critic of the Obama administration's nuclear deal with Iran. "It must be ripped up," Bolton tweeted in January.
Earlier on Sunday, Rouhani had told a gathering of Iranian diplomats that Trump shouldn't play with the lion's tail because that would "only lead to regret."
"America should know that peace with Iran is the mother of all peace, and war with Iran is the mother of all wars," said Rouhani, quoted by the state news agency IRNA.
The latest tit-for-tat exchange comes as Iranian officials threaten to block the Strait of Hormuz, a strategic choke point for oil shipments in the Persian Gulf region, in retaliation for proposed U.S. sanctions.
James Stavridis, retired four-star U.S. Navy admiral and NATO supreme allied commander, called the Strait of Hormuz a "flashpoint" for a potential conflict.
"Here's what drove that [Trump's] tweet: The Iranians are talking about closing that waterway and choking off oil if they are sanctioned. If they do that, and they've done it before, can you spell gas prices rising and disruption in the oil markets?" Stavridis said Monday on MSNBC's "Morning Joe."
"It is a very dangerous game of chicken to play," he added, saying that the U.S. must mend relationships with allies and partners before going "into another war in the Middle East."
Stavridis, dean of Tufts University's Fletcher School, said in an interview with CNBC on Monday that if Iran were to close the Strait of Hormuz, "the U.S. and our Arabian Gulf Allies would be able to open it in a matter of days."
In a blistering speech on Sunday, Secretary of State Mike Pompeo launched a rhetorical assault on Iran's regime, saying it "resembles the Mafia more than a government."
Pompeo, in a California speech to a largely Iranian-American audience, dismissed Rouhani and Foreign Minister Mohammad Javad Zarif, who negotiated the 2015 nuclear deal with the United States and other countries, as "merely polished front men for the ayatollahs' international con artistry."