US President Donald Trump on Monday called on Iran to stop supporting the Houthi rebels in Yemen, saying — in no uncertain terms — that he would hold Tehran responsible for any attacks carried out by them. 

The Houthis are an Iran-backed Shiite Muslim militia that has been fighting a civil war in Yemen since 2014. The group controls large swaths of the conflict-ridden country, including the capital Sanaa.

"Every shot fired by the Houthis will be looked upon, from this point forward, as being a shot fired from the weapons and leadership of IRAN, and IRAN will be held responsible, and suffer the consequences, and those consequences will be dire!" Trump wrote on his Truth Social platform.

Iran has long denied having influence on the Houthi rebels.

Response to Houthi attacks on trade ships

But experts say there is a link between Tehran and the Shiite militia.

"Alongside pro-Iranian groups in Iraq, the Houthi rebels are one of Iran's last active proxy groups in the region," said Hamidreza Azizi, an Iran expert at the German Institute for International and Security Affairs (SWP).

"Based on the talks in Iran that I am following, it seems some decision makers in Tehran want the Houthis to react to any US attack with a firm response and not show weakness," she said, adding: "In their eyes, Tehran would lose its strategic counterweight against the US in the event of a military defeat of the Houthis. And the next stop could be a direct attack on Iran."

The Houthis began attacking ships near the Red Sea and the Gulf of Aden in late 2023 in retaliation for Israel's ground offensive in Gaza.

The group has since been classified as a terrorist organization by the United States.

After a period of relative calm coinciding with the ceasefire in Gaza in January, the Houthis announced last week that they would resume attacks on Israeli ships sailing in the region.

This prompted Trump to order fresh strikes on the Houthis over the weekend.

Trump threatens war over nuclear program

Tehran has so far not ruled out the possibility of engaging in indirect negotiations with the US.

The two countries have not had diplomatic relations since 1980, but the Iranian leadership seems to be aware of the risks posed by the present situation.

At the start of March, Trump said he had sent a letter to Iran's Supreme Leader Ayatollah Ali Khamenei urging new talks on the country's nuclear program and warning of possible military action if this initiative gets refused.

"There are two options: military action or a negotiated solution," Trump said in an interview with US broadcaster Fox Business Network.

Tehran confirmed receiving Trump's letter. but gave no official response to it.

Ismail Baghai, spokesman for the Iranian Foreign Ministry, said on Sunday that Tehran was still thinking about its response. Iranian authorities, he added, had no intention of disclosing the contents of Trump's letter. 

"We don't know exactly what the letter says. But the signals from Tehran are contradictory," said SWP expert Azizi.

"While Khamenei continues to reject direct talks with the US, Tehran apparently wants to keep the door open for indirect negotiations," she said, pointing to a recent statement by Iranian Foreign Minister Abbas Araghchi. Talking to a local newspaper in early March, Araghchi said Iran was examining indirect channels of communication with Washington.

"Iran seems to be concerned about possible preconditions from the Trump administration for such talks,” Azizi noted, pointing out that Washington could demand that Tehran cease its support for its regional proxies as well as end its nuclear and missile programs.

The expert stressed that such conditions are unacceptable for Iran.

"I think Iran wants to hold talks with the US, but without any preconditions,” she said. "In this context, the importance of the trilateral meeting between Iran, China and Russia should also be emphasized. Tehran wants to secure the support of Russia and China in order to limit the talks to the nuclear program and, at the same time, signal to the US that it has alternative partners."

Beijing, Moscow close ranks with Tehran

Last week, senior diplomats from Iran, Russia and China held talks in the Chinese capital, where both Moscow and Beijing backed Iran and described Western sanctions against Tehran as "illegal."

They also called for increased diplomatic efforts to resolve the conflict over Iran's nuclear program.

During Trump's first presidential term, the US unilaterally withdrew from the 2015 international nuclear agreement with Iran. A year after the US withdrawal, Tehran began to gradually expand its nuclear research.

Many believe the country is now closer than ever to building a nuclear weapon.

Fears of conflict rise

According to the International Atomic Energy Agency (IAEA), Iran has increased the amount of highly enriched uranium in its possession to a dangerous level, opening the door to a possible military use. 

The agency said there is no credible civilian use for uranium enriched to 60%. Technologically, there is a relatively minor leap from 60% to the 90% threshold required to develop a nuclear bomb.

"Iran is the only non-nuclear weapon state enriching to this level, causing me serious concern," IAEA chief Rafael Grossi said at the beginning of March.

Tehran has continuously insisted that its nuclear program is for civilian purposes.

However, there have been contradictory statements from Iranian politicians in recent months, with some calling for a change to the nation's nuclear policy while others hinting at the possible development of nuclear weapons.

"Since the end of Hassan Rouhani's presidency in 2021, Iran has increasingly relied on threats and the use of its nuclear program as leverage," Behrooz Bayat, a former adviser to the IAEA, told DW.

"If this strategy is continued, there could be a further escalation. However, such a step would be extremely risky. But it cannot be completely ruled out," he added. "The coming weeks will be decisive. Whether negotiations or confrontation, Tehran's response will have a serious impact on peace and stability in the Middle East." 

The article was originally written in German.