Washington (CNN) President Donald Trump announced new sanctions against Iran Monday in part to retaliate after the downing of a US drone last week, with the punitive measures set to target Iran's Supreme Leader, military officials and its top diplomat, Foreign Minister Javad Zarif.

Speaking to reporters in the Oval Office, Trump said he signed an executive order imposing "hard hitting" sanctions on Iran that will deny Iran's Supreme Leader Ayatollah Ali Khamenei, his office "and many others" access to financial instruments.

"Today's actions follow a series of aggressive behaviors by the Iranian regime in recent weeks, including shooting down of US drones," Trump said, flanked by Treasury Secretary Steve Mnuchin and Vice President Mike Pence. "The supreme leader of Iran is one who ultimately is responsible of the hostile conduct of the regime. He's respected within his country. His office oversees the regime's most brutal instruments including the Islamic Revolutionary Guard Corps."

'America's desperation'

CNN's Frederik Pleitgen, speaking from Iran, said the state-backed press agency IRNA was denouncing the move as a sign of "America's desperation." And Zarif took to Twitter to blast Iran hawks he calls the "B Team" -- national security adviser John Bolton, the crown prince of Saudi Arabia Mohammed bin Salman and the crown prince of the United Arab Emirates Mohammed bin Zayed.

"It's now clear that the #B_Team is not concerned with US interests—they despise diplomacy, and thirst for war," Zarif said.

.@realDonaldTrump is 100% right that the US military has no business in the Persian Gulf. Removal of its forces is fully in line with interests of US and the world. But it's now clear that the #B_Team is not concerned with US interests—they despise diplomacy, and thirst for war. — Javad Zarif (@JZarif) June 24, 2019

Before the sanctions announcement, a senior Iranian official said the country's leadership sees "war and sanctions as two sides of the same coin" and stressed that Iran could not be forced into negotiations.

Speaking to reporters after Trump's announcement, Mnuchin said the new sanctions would "lock up literally billions of dollars of assets."

Mark Dubowitz, CEO of the Foundation for Defense of Democracies, said that the Ayatollah oversees an "estimated $200 billion corporate empire" that includes hundreds of companies with interests in agriculture, energy, real estate and other sectors.

People "are making a big mistake thinking these sanctions are just symbolic," Dubowitz said.

In his comments to reporters Monday, Mnuchin also appeared to break with a well-guarded policy of not commenting on future sanctions actions after he announced to reporters that Trump had also directed him to add Iran's foreign minister Javad Zarif to the US governments sanction's list "later this week."

The US government has traditionally closely guarded sanctions plans to avert the possibility of an individual or entity taking any steps to evade the impact of being cut off from the US financial system.

A Treasury spokesman could not be immediately reached by CNN on the matter.

Mnuchin offered no detail on the plan to penalize Zarif, or the impact of sanctioning Iran's top international diplomat who regularly travels abroad -- including to the US and its allies -- to engage in diplomacy. Sanctions can include a travel ban, as well as financial measures.

Nor did Mnuchin explain how sanctions against Zarif align with the Trump administration's assertion that it is interested in diplomacy with Iran and the President's repeated declarations that he is ready to talk. Trump was asked during an NBC interview aired Sunday if he had conditions for talking with Tehran and said, "not as far as I'm concerned, no preconditions."

Hagar Hajjar Chemali, a former spokesperson for the US mission to the UN, said the move against Zarif is "a message that they're not interested in negotiating anytime soon, because they are in effect sanctioning Iran's chief negotiator. If Iran comes back to the table, the person who's going to be tasked with leading those negotiations is certainly Foreign Minister Zarif."

The sanctions against Zarif will make his travel to the US more difficult, said Chemali, a former director for Syria and Lebanon at the National Security Council and former Middle East policy adviser at the Treasury Department. She pointed out that Zarif comes to the US to attend the UN General Assembly every September.

To attend, Zarif may now need a waiver that it isn't clear the Trump administration will grant.

Secretary of State Mike Pompeo, speaking to reporters Sunday, echoed that "we're prepared to negotiate with no preconditions," adding that he was "confident that at the very moment they are ready to engage with us, we will be able to begin these conversations."

Pompeo has issued 12 demands for change in Iran before the US will ease its maximum pressure campaign against Iran. The Trump administration has argued that the Joint Comprehensive Plan of Action, the nuclear deal it abandoned in 2018, is inadequate as it doesn't cover Iran's ballistic missiles or regional activities.

'War and sanctions'

Even though the International Atomic Energy Agency has found that Iran has complied with the deal, the US has re-imposed all sanctions in place before the deal and added new ones. Those actions have undermined the central concept of the deal -- that in exchange for controls on its nuclear program, Iran would see some economic relief.

Before Monday's sanctions were announced, Iranian officials issued an apparent rebuff to Trump's comments to NBC on talking without preconditions and said they wouldn't be forced to the negotiating table.

An adviser to Iranian President Hassan Rouhani tweeted Monday that "we are neither warmongers nor do we deserve sanctions."

"But we consider war and sanctions as two sides of the same coin," said Hesameddin Ashena, the adviser, in the tweet. "America's claim to negotiate without preconditions is unacceptable while threats and sanctions continue. They must give us more than JCPOA if they demand for something more than this agreement."

US allies didn't immediately respond for comment about the planned sanctions against Zarif. A UK official said that "the UK remains fully committed to the nuclear deal -- which includes sanctions relief -- for as long as Iran remains in compliance. To date Iran has upheld its commitments. While we share US concerns about Iran and its regional behavior, our difference in approach to the nuclear deal and sanctions is well known."

The UK has over 200 EU sanctions listings in place against Iran for nuclear-related and ballistic missile activity, including against the Islamic Revolutionary Guard Corps in its entirety, the official said.

On Monday, Trump said the newly announced sanctions "deny the Supreme Leader and the Supreme Leader's office and those closely affiliated with him and the office access to key financial resources and support. The assets of Ayatollah Khomeini (Khamenei) will not be spared from the sanctions."

Chemali said that if the targeted Iranian officials "actually have assets and funds located in any banks abroad, then they're going to move that just to ensure that there's no way that account can be closed or anyone could get their hands on it. That's one of the reasons why Treasury doesn't usually preview sanctions is to prevent capital flight."

While Trump called the sanctions a "strong and proportionate response," neither he nor Mnuchin would offer exact details about what the retaliation was for. Trump said, "this was something that was going to happen anyway."

Mnuchin said "some of this was in the works, some of this was a result of recent activities. I'm not going to identify which is which."

The lack of clarity might be a result of Trump's moves to downplay the impact of the drone strike, which he called "a new wrinkle" shortly after it happened.

After Trump halted plans for a military strike against Iran in retaliation for the attack on the drone, Trump said he found it hard to believe it had been an "intentional" act. "I think that it could have been somebody who was loose and stupid that did it," Trump said in the Oval Office on June 20.

Mnuchin and the Treasury Department also announced sanctions against eight senior commanders of Navy, Aerospace, and Ground Forces of the Islamic Revolutionary Guards Corps, the elite military unit with deep political influence and interests in wide parts .

"These commanders sit atop a bureaucracy that supervises the IRGC's malicious regional activities, including its provocative ballistic missile program, harassment and sabotage of commercial vessels in international waters, and its destabilizing presence in Syria," a Treasury statement said.