Saudi Arabia’s foreign minister warned on Monday the kingdom would respond to the “aggression” of Iranian support for an uprising in neighboring Yemen, saying “necessary measures” could be taken if diplomacy failed.

Prince Saud bin Faisal Al Saud was speaking alongside Britain’s visiting foreign secretary, Philip Hammond, in Riyadh. Hammond said, “None of us wants to see military action.”

Earlier in the day, the foreign minister of Yemen’s internationally-recognized government had called on nearby Arab Gulf states to intervene. “They’re expanding in territory, occupying airports and cities, attacking Aden with planes,” Riyadh Yassen said, referring to the Shia Houthi rebels who first seized the capital, Sana’a, late last year.

Yassen also told Al Jazeera that Iran was behind the Houthi takeover.

Yemen has slid into a civil war since President Abd Rabbuh Mansur al-Hadi fled Sana’a and set up a government-in-exile in the port city of Aden. He is supported by neighboring Sunni powers and the West but increasingly cornered. His forces must see off attacks not only from the Houthis, who control the entire northwest of the country, but from supporters of his predecessor, Ali Abdullah Saleh, as well.

Clashes were reported in Aden over the weekend after suicide bombers killed and wounded hundreds in attacks on two mosques in the capital on Friday. An unidentified warplane attacked Hadi’s residence in Aden.

Hadi and his supporters see the Houthis as agents of Iran. Although it is unclear to what extent the two coordinated before the rebels dissolved parliament in February and placed Hadi under house arrest, the Shia state has helped them consolidate their position in Sana’a since. A delegation of Houthi leaders traveled to Tehran earlier this month. Iranian medical supplies arrived in Yemen a day after the two regimes signed an aviation agreement.

Hadi still commands the loyalty of local authorities in the Hadhramaut, Ma’rib and Shabwah provinces which contain most of Yemen’s oil and natural gas reserves. But he has failed to win over factions that advocate the secession of the former South Yemen as well as members of Saleh’s clan. Their refusal to support him allowed the Houthis to take over Sana’a in the first place.

Al Qaeda could take advantage of the chaos. The international terrorist group’s Yemen branch is considered by Western experts to be its most dangerous.

Military intervention by Arab powers looks unlikely in the short term but would hardly be unprecedented. In 2011, forces from Saudi Arabia and the United Arab Emirates entered Bahrain to put down protests led by the island’s majority Shia community. Warplanes from Gulf states have also participated in American-led strikes against the Islamic State in Iraq and Syria while Emirate jets recently carried out attacks in Libya against the positions of a rival Islamist government in Tripoli.

In 2012, the monarchies forced Yemen’s Saleh to step down after more than two decades in power, fearing an “Arab Spring”-style uprising in the country. Saleh had presided over the unification of Yemen in 1990. The south seceded four years later, triggering a civil war and northern occupation in 1994.