Iran said Tuesday new US sanctions against its leaders marked the end of diplomacy with Washington, after President Donald Trump threatened the country with obliteration.

Trump imposed new sanctions Monday against Iran's supreme leader Ayatollah Ali Khamenei and top military chiefs, further raising the stakes in an escalating regional standoff.

The US Treasury said it would also blacklist Iran's Foreign Minister Mohammad Javad Zarif - a moderate figure and key architect of the 2015 Iran nuclear deal - and eight top commanders from Iran's Revolutionary Guards.

Iran's Foreign Ministry spokesman Abbas Mousavi said Tuesday that "imposing fruitless sanctions against Iran's supreme leader and the commander of Iran's diplomacy is the permanent closure of the path to diplomacy with Trump's desperate government."

"Trump's government is destroying all established international mechanisms for keeping global peace and security," he said in a tweet.

China on Tuesday urged "calm and restraint" as tensions between the US and Iran escalate following US President Donald Trump's new sanctions on Iran.

"China firmly opposes unilateral sanctions and the so-called long-arm jurisdiction, we believe that blindly applying maximum pressure will not help solve the problem," said Chinese Foreign Ministry spokesman Geng Shuang at a press briefing in Beijing.

"Facts have proved that these measures have had the opposite effect and aggravated regional unrest," he added.

Washington's move came after Iran shot down a US spy drone last week and Trump planned a retaliatory strike, and canceled it at the last minute. 

That follows a series of attacks on ships in sensitive Gulf waters which the US has blamed on Iran - claims hotly denied by Tehran.

US media have also reported Trump secretly authorised cyber-attacks against Iran's missile defence systems and a spy network, but Tehran says no damage was done.

"We hope that the parties concerned will maintain calm and restraint and avoid further escalation of tension," Geng said.

Trump called Monday's sanctions a "strong and proportionate response to Iran's increasingly provocative actions."

"We do not ask for conflict," Trump said, adding that depending on Iran's response the sanctions could end tomorrow or "years from now."

Tehran and Washington broke off diplomatic relations in 1980 over the hostage crisis at the US embassy in Tehran following Iran's Islamic revolution.