National Security Advisor John Bolton (R), listens to U.S. President Donald Trump as he speaks about the FBI raid at lawyer Michael Cohen's office, while receiving a briefing from senior military leaders regarding Syria, in the Cabinet Room, on April 9, 2018 in Washington, DC. Getty Images

National security advisor John Bolton on Monday doubled down on President Donald Trump's all-caps tweet directed at the Iranian regime. 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. TWEET 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 history of tough talk

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." TWEET Bolton was also a vocal critic of the Obama administration's nuclear deal with Iran. "It must be ripped up," Bolton tweeted in January.

'Mother of all wars'