US President Donald Trump announces new sanctions against Iran in response to one of its unarmed drone downed by Iran.

In a press conference, Trump said sanctions were inevitable after Iran downed one of US-owned unmanned aircraft (UAV).

The sanctions have targeted the office of Khamenei, Iran's foreign minister and senior commanders of the Iranian Revolution Guards Corps (IRGC).

"We do not seek conflict with Iran or any other country," Trump said. "I can only tell you we cannot ever let Iran have a nuclear weapon."

"We will continue to increase pressure on Tehran until the regime abandons its dangerous activities," he said.

Trump said the supreme leader and his associates were ultimately responsible for what the US president called "the hostile conduct of the regime".

"Sanctions imposed through the executive order will 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," Trump said.

He added that the sanctions have nothing to do with the Tehran's downing of a surveillance US drone last week.

Shortly after Trump signed the order, US Treasury Secretary Steven Mnuchin said that some of the sanctions were in the works before the drone was shot down.

He added that later this week sanctions will also be imposed on Iranian Foreign Minister Mohammad Javad Zarif.

"We have literally locked up tens and tens of billions of dollars," Mnuchin said in the White House briefing room. "These sanctions are highly effective."

Sanctions were also imposed on eight senior commanders of Navy, Aerospace, and Ground Forces of the IRGC, the US Treasury Department said in a statement.

"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," the statement read.

Zarif on Monday reiterated the country’s stance on Washington’s economic sanctions against Tehran and said Iran is resolved to resist such pressures "with full power".

Responding to the sanctions announcement, Iranian Foreign Minister Zarif tweeted that hawkish politicians close to Trump were thirsty for war rather than diplomacy.

Tensions between the United States and Iran that have grown since May, when Washington ordered all countries to halt imports of Iranian oil. (ILKHA)