The United States on Monday imposed new sanctions on Iran targeting its Supreme Leader Ayatollah Ali Khamenei and other senior officials, a move further worsening the already strained Washington-Tehran ties.

US President Donald Trump signed an executive order on Monday at the White House, which he said is "imposing hard-hitting sanctions on the supreme leader of Iran and the office of the supreme leader of Iran and many others."

Trump accused Khamenei of being ultimately "responsible for the hostile conduct of the regime."

The newly added sanctions will deny Iranian leadership's access to financial resources, blocking them from using the US financial system or accessing any assets in the United States, according to the White House.

US Treasury Secretary Steven Mnuchin revealed in a following press conference on Monday that the new order will freeze billions of additional dollars in Iranian assets.

Mnuchin also said Trump had instructed him to designate Iranian Foreign Minister Mohammad Javad Zarif "later this week." The new order allows Mnuchin to impose sanctions on officials appointed to their position by the Iran's supreme leader.

Facing mounting US pressure, Zarif, in response to the new sanctions, tweeted that the hawkish senior US officials close to Trump "despise diplomacy, and thirst for war."

"Nobody in a clear mind can accept to have a dialogue with somebody that is threatening you with more sanctions," Iran's ambassador to the United Nations Majid Takht Ravanchi told reporters on Monday.

Ties between the United States and Iran have deteriorated after Washington walked away from the landmark 2015 Iran nuclear deal in May 2018 and reimposed energy and financial sanctions, which had been removed under the deal, on Iran.

Iran has suspended parts of its commitments subject to the nuclear deal and have threatened to go further.

Tensions between the two countries remain high as Washington continued to tighten sanctions against Tehran and the two sides traded barbs.

Last week, the Iranian Islamic Revolutionary Guard Corps (IRGC) shot down a US drone, which Iran said had crossed Iranian borders.

Tehran will take judicial measures concerning the US move in deploying a "spy drone into Iranian airspace as a violation of the international law," said Laya Joneidi, vice president for legal affairs in the Iranian administration.

But the United States said the drone, a US Navy RQ-4A Global Hawk, was flying over international waters when it was downed.

The United States also carried out cyber attacks against Iranian missile control systems last week, an action which Iran said on Monday had failed.

Iranian Minister of Information and Communications Technology Mohammad Javad Azari Jahromi also decried US cyber attacks on Iran over the past years, saying that "We have been facing cyber-terrorism for a long time."

Earlier this month, the United States claimed Iran is responsible for an attack on two oil tankers in the Gulf of Oman. The accusation was dismissed by the Islamic Republic.

Over the accusation, Zarif has said the United States immediately jumped to make allegations against Iran was a plan to use sabotage diplomacy to cover up its economic terrorism against Iran.

Following the attack on the oil tankers, the Pentagon authorized the deployment of about 1,000 additional troops to the region for so-called "defensive purpose."

This was preceded by the deployment of the Abraham Lincoln aircraft carrier group, bombers, the amphibious transport dock and Patriot air defense system to the region in early May.