A mere forty-eight hours after the Houthis stormed the presidential palace in Sana’a last month, virtually the entire Yemeni government offered its resignation. The question of the Houthis’ alleged ties to Iran immediately took on new significance. Indeed, evidence of Tehran’s support for its co-religionist rebels in Yemen is growing.

The Houthis are an organic part of Yemeni society, hailing from the Zaydi sect of Shi’a Islam that ruled Yemen in the mid-20th century. Marginalized by the government of former president Ali Abdullah Saleh, and opposed to his close ties to the U.S. post-9/11, the Houthis fought six wars with the Yemeni military between 2004 and 2010. Accusations of Iranian support for the Houthi rebels in northern Yemen have mounted ever since.

In October 2009, Yemen seized an arms-laden Iranian ship manned by Iranian weapons experts sent to replace other Iranians fighting alongside the Houthis. A few months later, reports emerged of a secret meeting along the Yemeni-Saudi border between Houthi rebels, Iran’s Islamic Revolutionary Guard Corps (IRGC), and the Lebanon-based Iranian proxy Hezbollah.

In January 2013, a joint U.S.-Yemeni military operation seized yet another ship, the Jihan 1, containing a cache of weapons off the coast of Yemen. The cache included weaponry such as Katyusha rockets (a favorite of Hezbollah), heat-seeking surface-to-air missiles, Iranian-made night-vision googles, and “artillery systems that track land and navy targets 40km away.” According to Yemeni officials, the interdicted ship was also carrying silencers, RDX and C-4 explosives, and ammunition. Despite Iranian denials, markings on the weapons indicated they had come from IRGC facilities. U.S. officials reported that the weapons were headed to the Houthis in Yemen’s northern provinces.

American and Yemeni forces who boarded the Jihan 1 also discovered ten wooden crates bearing Chinese stencil marks containing QW-1M man-portable air-defense systems (MANPADS) that had only recently been built by the state-owned China Precision Machinery Import and Export Company. Leaked documents indicate that the U.S. government has been aware of a history of Chinese arms sales to Iran that have made their way to Shiite insurgents in the Middle East.

In late 2014, alarm bells rang throughout the region as reports emerged that the Houthi rebels had received “shipments of heavy weapons” from an allied Islamic country via the port of Hodeidah, which the rebels seized in October. Concerns mounted that the rebels’ continued control over Hodeidah, Yemen’s fourth largest city and a strategically significant port city on the Red Sea, would continue to facilitate the flow of illicit weapons in support of their military expansion.

Iran’s transfer of weapons to the Houthi rebels not only jeopardizes the political stability of Yemen and threatens the strategic trade routes linking the Red Sea to the Gulf of Aden, but is also in violation of recognized international agreements. Iran is prohibited from supplying, selling, or transferring “directly or indirectly…any arms or related material” according to United Nations Security Council Resolution (UNSCR) 1747 passed in March 2007.

There are now several indications that the Iranians have not only supplied the Houthis but trained them as well. Yemeni officials claimed that Houthis have been traveling to Lebanon and Iran for training for over a year. These officials even claimed that 100 Houthi fighters trained in Iran in 2014 alone.

Additionally, a senior Iranian official admitted in December 2014 that the IRGC’s Qods Force, charged with external operations, sent a “few hundred” military personnel to directly train Houthi combatants in Yemen, in addition to about a dozen Iranian military advisers already on the ground.

In 2012, U.S. officials noted that along with weapons, Iran had been regularly sending several million dollars in cash to Yemen to back the Shi’ite rebels. Just last month, a Yemeni official warned that “sacks of cash” from Tehran had been arriving at Sana’a International Airport, some of which was channeled via Hezbollah. The Houthis have also received communications support from Hezbollah, which helped establish and support Al Masira, the Houthi radio and television station based in their northern stronghold of Sa’ada.

When the Houthis seized the Yemeni capital in late September, Iranian officials could hardly contain their excitement. Days later, Ali Riza Zakani, a prominent member of the Iranian parliament exclaimed, “Three Arab capitals have already fallen into Iran’s hands,” and implying that after Damascus, Beirut, and Baghdad, Sana’a would be next. Zakani added that the Houthi rebellion in Yemen is “a natural extension of the Iranian revolution.” Ali Akbar Velayati, a close adviser to the Supreme Leader, announced, “Iran supports the rightful struggles of Ansar Allah [the Houthis’ official name] in Yemen and knows this movement to be part of the successful movements of the Islamic Awakening.”

Just days after the Houthis marched into Sana’a chanting their usual slogan of “Death to America, Death to Israel,” the rebels made it their first order of business to free the ten jailed crew members of the Jihan 1, including two suspected Hezbollah operatives.

Since their seizure of Sana’a, the Houthis have made efforts to distance their movement from its sectarian identity, rallying behind an agenda of political reform and confronting corruption. But just last month, a website close to the IRGC published a three-pronged strategy guide to ensure full Houthi control over Yemen.

While the story behind Yemen’s Houthi crisis is not yet written, Tehran’s fingerprints are undeniable. And although the Houthis are not an Iranian transplant, there is ample reason to be concerned that their ascent to power will translate into an expansion of Iranian influence in the Arabian Peninsula.

Oren Adaki is a Research Analyst at the Foundation for Defense of Democracies.