Officials in Iran lashed out on Tuesday at the latest round of sanctions imposed by the Trump administration, casting doubt on any hope of an imminent diplomatic end to the standoff over the Islamic Republic's nuclear program. President Hassan Rouhani called the new U.S. sanctions "outrageous and idiotic," and suggested the Trump administration was "afflicted by mental retardation" for imposing them.

The country's foreign ministry spokesman said the latest move by the U.S. brought a "permanent closure" to any hope of diplomacy between the two nations.

President Trump imposed the new sanctions on Monday. For the first time they target Iran's Supreme Leader Ayatollah Ali Khamenei directly, barring his access to the international financial system. The punitive measures -- which add to a long list of financial sanctions already slapped on Tehran by Mr. Trump since he pulled the U.S. out of the nuclear deal with Iran last year -- also target other officials.

Rouhani mocked Mr. Trump over the sanctions, saying: "You sanction the foreign minister simultaneously with a request for talks?"

CBS News White House correspondent Ben Tracy says the latest statements from Iran are further evidence that President Trump's strategy, of forcing the Islamic Republic to change its behavior by strangling its economy, is not working.

"Who knows what's going to happen," Mr. Trump said Monday. "I can only tell you we cannot ever let Iran have a nuclear weapon."

Instead of using force, President Trump put on a show of it in the Oval Office on Monday, signing the sanctions order in front of cameras, flanked by his vice president and treasury secretary. The sanctions target the ayatollah and at least eight Iranian military commanders, including the official the U.S. blames for the shooting down an American drone last week.

President Trump said Monday that he would "love to be able to negotiate a new deal" on Iran's nuclear program "if they want to."

"If they don't want to, that's fine too," the president said. "Frankly they might as well do it soon."

The U.S. has now imposed almost 1,000 specific sanctions on Iran since pulling out of the nuclear deal, and they are taking a toll on the Iranian people and economy. The value of the Republic's currency has dropped 60%, and inflation is at more than 40%.

"You cannot start a dialogue with somebody who is threatening you, who is intimidating you," Iran's Ambassador to the United Nations said on Monday, warning that tension between the two countries was "really dangerous."

Iran has dismissed the U.S. offer of direct negotiations as a lie, citing the Trump administration's mounting sanctions regime.

Instead of negotiating, Iran is retaliating. It has allegedly attacked a total of six tankers in and near the Persian Gulf in recent weeks, and the U.S. insists it shot down the American spy drone in international airspace. Tehran is also threatening to enrich more uranium to a level much closer to that which would make it usable as fuel for a nuclear weapon.

Suzanne Maloney, an Iran expert at the Brookings' Center for Middle East Policy who previously worked at the State Department, said Tehran is clearly trying "to turn up the heat, to see if the president will respond."

President Trump has warned that if he does decide to change his approach, he does not need congressional approval to order a military strike.

"I do like keeping them abreast," the president said, "but I don't have to do it, legally."

Mr. Trump has said the only precondition to open a dialogue with Iran is that it won't be allowed to develop a nuclear weapon -- but the nuclear deal the president pulled out of last year prevented exactly that, and the Iranians insist they do not want an atomic bomb. The foreign minister reiterated on Tuesday his country's assertion that it would "never" seek to acquire a nuclear weapon.

America's allies around the world are not on board with the new sanctions, and the rising tension is likely to be one of many issues discussed later this week when the U.S. meets in Japan with other G-20 nations.

A senior politician in Britain suggested on Tuesday that if the Trump administration were to go to war with Iran, it might have to do so without the backing of one of America's closest allies.

"The U.S. is our closest ally, we talk to them the whole time, we consider any requests that they say carefully," Foreign Minister Jeremy Hunt said in Parliament on Tuesday. "But I cannot envisage any situation where they request or we agree to any moves to go to war."

Hunt, one of two men vying to take over as British Prime Minister when Theresa May steps down next month, said "the message we are sending with our partners in the European Union, particularly the French and the Germans, is that with respect to Iran's nuclear programme, this is a crucial week... It is absolutely essential that they (Iranians) stick to that deal in its entirety for it to preserve and for us to have a nuclear free middle east.