Iran has warned the United States that it is ready for war if Washington wants to "test" it, as US President Donald Trump on Monday escalated pressure, claiming any country doing business with Iran will face a 25 percent tariff on any trade with the US, coupled with potential military action.

Trump, who views tariffs as a potent tool to coerce others into bending to his will, announced the new levies via social media, stating they would take effect "immediately". Oil prices climbed on Tuesday, a direct reaction to market jitters given Iran accounts for 3 percent of global oil production.

China was quick to denounce the measure, vowing to take all necessary measures to safeguard its legitimate rights and interests.

Foreign Ministry spokeswoman Mao Ning told reporters on Tuesday, "China's position on the tariff issue is very clear that there are no winners in a tariff war. China will resolutely safeguard its legitimate rights and interests."

Meanwhile, the US virtual embassy in Iran on Monday urged its citizens to leave the country immediately by land for Armenia or Turkiye. With no physical US embassy or consulate operating in Iran, the Swiss embassy acts as the protecting power of US interests there.

Mao said China is closely monitoring the situation in Iran, and will take all necessary measures to protect the safety of Chinese citizens. "China has always opposed interference in other countries' internal affairs and the use or threat of use of force in international relations. China hopes that all parties will do more things conducive to peace and stability in the Middle East," she said.

The new tariff piles additional pressure on Iran, coming on the heels of Trump's threats on Sunday that his administration is weighing "some very strong options", including potential military actions.

In an interview with Al Jazeera on Monday, Iranian Foreign Minister Abbas Araghchi said the channels of communication with the US were open, but stressed that his country was "prepared for all scenarios", claiming that Iran now has "large and extensive military preparedness" compared to last year's 12-day war with Israel.

The New York Times reported on Monday that the Pentagon is presenting Trump with a "wider range of strike options" on Iran than previously reported. Last year, the US joined Israel's war against Iran by conducting airstrikes on Iranian nuclear facilities.

Possible targets

According to the report, which cited a US official, possible targets include Iran's nuclear program and ballistic missile sites. However, the official noted that narrower options, including a cyberattack or a strike against Iran's domestic security apparatus, are more likely.

"If Washington wants to test the military option it has tested before, we are ready for it," said Araghchi, adding that he hoped the US would choose "the wise option" of dialogue, while warning of "those trying to drag Washington into war and serve Israel's interests".

White House Press Secretary Karoline Leavitt told reporters on Monday that "airstrikes are among the numerous options on the table for the commander-in-chief", but diplomacy is always the first option with Trump.

Protests have erupted in several Iranian cities since late December over the sharp fall in the national currency rial and long-standing economic hardships. The reported death toll from the unrest on both sides of the security forces and civilians is mounting.

State media reported that tens of thousands of pro-government demonstrators took to the streets of Tehran on Monday, waving Iranian national flags to condemn the US and Israel for "instigating unrest" in the country over the past two weeks.

"These massive rallies have thwarted the plans of foreign enemies that were supposed to be carried out by domestic mercenaries," said Supreme Leader Ali Khamenei, as quoted by state television.

In the Al Jazeera interview, Araghchi said his communications with US special envoy Steve Witkoff over nuclear talks had "continued before and after the protests and are still ongoing".

But he questioned whether the US was "ready for fair and just negotiations", as Washington's proposed ideas and threats against Iran are "incompatible".

Zhang Yunbi in Beijing contributed to this story.