The report suggests that Iran has sent advisers from Shiite proxies, including Afghan forces, to train Houthi units and provide logistical support. The report says, ”The deployment of interoperable proxy forces is part of Iran’s evolution of a form of hybrid warfare that will allow it to project significant force far from its borders and fundamentally alter the balance of power in the region.”

One of the report’s authors, Emily Estelle, says the presence of Afghan advisers, including some who fought in Syria under the leadership of Iran’s special forces unit the Quds Force, might indicate a change. She said, “This deployment is an early indicator that Iran may be mobilising its proxy network to conduct hybrid warfare in Yemen as it has in Syria, albeit on a much smaller scale.”

The report explains how Houthi forces are using what appears to be Iranian-supplied drone technology. Iran and the Houthis are facing off against Saudi Arabia and an Arab coalition, part of a regional power struggle that is also exacerbating the conflict in Syria.  Evidence has emerged that Tehran has increased its support to the Houthis, who seized the capital Sanaa in 2014.

Weapons experts have described the ways in which a Yemeni-built Qasef-1 drone shares specifications with an Iranian model and has been used to destroy air defence systems installed by the Saudi-led coalition. The same drone model might have been used in an attack that killed more than 20 troops who were loyal to president Abdrabu Mansur Hadi, two weeks ago.

Iran has been accused of supplying the technology that allowed Houthi forces to use a remote-controlled boat to attack a Saudi vessel in the Red Sea last January. 

It is believed that the Iranian Revolutionary Guards and the Quds Force supplied penetrators, a type of armour-piercing projectile, for use in improvised explosive devices. A UN Security Council report confirmed the connection in January.

The Houthis, a Zaidi Shiite minority, launched a series of rebellions against the government of Ali Abdullah Saleh in 2004, and forced him from power in 2011 during the Arab Spring. His successor, Mr Hadi, struggled to assert control as he dealt with a southern separatist movement and Al Qaeda at a time when members of his security forces remained loyal to Mr Saleh.

In September 2014, Houthi fighters took control of Sanaa, prompting the intervention of a Saudi-led coalition of nine Middle East and African countries, including the UAE, six months later. Two months after the coalition intervened, Mr Saleh formally announced his alliance with the Houthis.

Government forces in the south and east remain in control of most of Yemen’s territory today, while the Houthis and their allies hold population centres in the northwest, including the capital.

More than 10,000 lives have been claimed by the conflict, which has also pushed Yemen to the brink of famine. According to Oxfam. Two-thirds of the population is classed as “food insecure”.

The report also made recommendations to Donald Trump’s administration. This week it emerged that the US was considering offering additional support in the form of intelligence and planning to the Saudi-led coalition as Washington continues its review of Yemen policy.

Yemen has been viewed s as a haven for Al Qaeda in the Arabian Peninsula. However, the Trump administration is increasingly focused on the threat posed by Iran.

Ms Estelle said the US should work to avoid isolating the Houthis and focus on reducing their reliance on Tehran. “This will require the US to steer the Saudi-led coalition’s operations in Yemen away from the pursuit of the Houthis’ total defeat,” she said. “The US should instead shape coalition operations to block Iranian expansion, prevent harm to Yemen’s civilian population, and pressure the Al Houthi-Saleh faction with the goal of bringing the combatants to the negotiating table.”

Other countries are concerned that Iran is breaching an embargo on supplying weapons to the Houthi movement. According to Reuters, a spokeswoman for Britain’s foreign office said last week that it was “concerned by Iranian support to the Houthis, including reports that Iran has transferred weapons to Yemen, which would be contrary to UN Security Council Resolution 2216 and the Security Council’s embargo on the export of weapons by Iran”.