Yemen’s president, Abd Rabbuh Mansur al-Hadi, resigned on Thursday, leaving Houthi rebels from the north in control of the capital and possibly the country’s political future.

constitutionally, Hadi’s resignation hands the presidency to the speaker of Yemen’s parliament until new elections can be called. But de facto, the Houthis, a Zaidi Shia rebel group from the former Yemen Arab Republic that is supported by Iran, seemed in control.

The Houthis first seized Sana’a, the capital, in September and had held Hadi a virtual prisoner in his palace since.

Prime Minister Khaled Bahah and his government also stepped down on Thursday, depriving the United States, which has regularly carried out airstrikes against suspected Islamic terrorists in the country, of any ally in Sana’a.

The Houthi takeover also raised the risk of insurgency in the south where separatists and Al Qaeda terrorists battled Hadi’s administration for their own reasons. The government deployed troops to the Aden and Lahij Governorates, both situated on the Gulf of Aden, late last year.

Both the Houthis and the militants in the south rejected Hadi’s proposed constitutional changes.

Hadi, a southerner himself who came to power after veteran president Ali Abdullah Saleh was forced to resign in 2012 amid protests inspired by “Arab Spring” uprisings across the region, wanted to split Yemen into six autonomous regions. The formerly communist South Yemen would be divided into two regions: Aden in the west and Hadhramaut in the east. The more populous former North Yemen would be split into four regions.

Southerners rejected the partition plan, fearing it would dilute their authority, especially over oil reserves in the Hadhramaut area.

The Zaidi rebel leader, Abdul-Malik al-Houthi, insisted on a unitary state, seeing Hadi’s plan as an attempt to strengthen Sunni and pro-Saudi fiefdoms in the rest of the country.

Saudi Arabia backed the southern separatists during Yemen’s 1994 civil war but later threw its weight behind Saleh and Hadi.

The desert kingdom, whose ruler, King Abdullah, died on Friday and was succeeded by his younger brother, Salman, sees the power struggle in Yemen within the context of its regional standoff with Iran. The two powers also back opposing sides in conflicts in Lebanon and Syria.