Washington: Tensions between the US and Iran escalated on Friday as President Donald Trump prepared new sanctions and told Tehran it was "playing with fire," prompting Iran to respond that it won't be bullied.
The deterioration in relations came as the US paved the way to punish Iran for testing a ballistic missile on Sunday.
As many as 17 entities connected with Iran's missile work and up to eight linked to terrorism would be named under penalties as early as Friday, according to two people familiar with US strategy.
Shortly after Mr Trump's intervention, Iran's foreign minister, Mohammad Javad Zarif, tweeted: "Iran unmoved by threats as we derive security from our people."
He added later: "We will never use our weapons against anyone, except in self-defence."
Iran earlier this week shrugged off Mr Trump's tough talk as the workings of an "inexperienced president".
Mr Trump's Iran tweet was one in a series of messages posted early on Friday morning, their themes varying from relations with Australia to university protests and Arnold Schwarzenegger's performance on the latest series of The Apprentice.
New sanctions
The Trump administration has adopted a hard line on Iran since taking power on January 20, banning its citizens from entering the US and accusing the nation of interfering in the affairs of the US's regional allies in the Middle East.
While such an approach could satisfy hawks in Washington who were never comfortable with former President Barack Obama's tentative rapprochement with Iran, it could also unsettle domestic Iranian politics where President Hassan Rouhani is hoping for re-election in May.
The new sanctions aren't designed to take aim at Iran's nuclear program, according to the people familiar with Washington's plans.
Under that agreement, signed with six countries including the US and Russia, Mr Obama eased some restrictions in exchange for Iran's promise not to develop nuclear weapons. While the missile test didn't contravene that deal directly, it may be seen as going against a UN Security Council resolution that enshrines it.
"The two sides will do what they can to harm each other without touching the nuclear agreement," said Adnan Tabatabai, chief executive officer of the Germany-based Centre for Applied Research in Partnership with the Orient.
Ending Iran's international isolation has paved the way for the country to increase oil exports, one of the reasons the price of crude has been depressed in the past year and a half. The latest round of US-Iranian tensions reverberated in oil markets on Friday as futures headed for a third weekly gain.
Tense relations
Even before the missile tests, bilateral relations were getting tense. Last month, Mr Trump named Iran among seven Muslim-majority countries whose citizens are temporarily barred from entering the US, and Tehran retaliated with a similar ban on Americans.
A bipartisan group of 22 US senators, including Republican Bob Corker, chairman of the Senate Foreign Relations Committee, and the panel's top-ranking Democrat, Ben Cardin, wrote a letter to Mr Trump on Thursday calling for the imposition of additional sanctions on Iran in response to the missile test.
But there may be a limit to how far Iran will want things to escalate. The country has urged the US not to overreact to its missile tests, Defence Minister Hossein Dehghan said in comments published by local news agency Tasnim.
While Mr Rouhani, the architect of the nuclear deal, and his inner circle will try to keep their responses to Mr Trump measured in order to avoid inflaming tensions, they can't stop other more hardline voices from speaking out.
On Friday, cleric Ayatollah Ahmad Khatami said that the message the Trump administration is sending constitutes a "struggle against religion, struggle against Islam, and altogether a very outdated message."
Empowering hardliners
Emboldening Iranian politicians that oppose a detente with the US threatens Mr Rouhani's chances for re-election and risks leading to the emergence of a more confrontational leader. Since the nuclear accord, Iran has still faced stumbling blocks at reopening its economy to the world as many investors remain hesitant, and the new sanctions risk further hindering appetite.
Supreme Leader Ayatollah Ali Khamenei, the highest authority in Iran and who has maintained the US can't be a trusted partner, has yet to comment.
"The perception that the US might be back rolling on the Iran deal and the anti-Iran mood that is emerging in Washington will further empower hardliners in Iran, where the rhetoric will be 'we told you so that these people cannot be trusted,'" said Maha Yahya, director of the Carnegie Middle East Centre in Beirut.
Bloomberg