Houthi rebels from the north of Yemen stormed President Abd Rabbuh Mansur al-Hadi’s residence in Sana’a on Tuesday after some of the worst fighting in the capital in years.

On Monday, security forces loyal to Hadi fought artillery battles near the presidential palace with militias from the north that first seized the capital in September.

The Houthis, a Zaidi Shia rebel group from the former Yemen Arab Republic, forced Hadi to appoint a new government at the time and fought off Sunni tribesmen allied to the international terrorist group Al Qaeda in the west and south.

The Houthi takeover fueled rumors of an imminent southern insurgency. Hadi’s government deployed troops to the Aden and Lahij Governorates, both situated on the Gulf of Aden, in anticipation of a separatist uprising there.

Seen as allies of Iran in its regional struggle for influence with Saudi Arabia, the Houthis said on Monday they would escalate the situation in the capital if their demands in a dispute over a draft constitution were not met.

Hadi has proposed to split the country into six autonomous regions in an attempt to appease separatists in the north and south. 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 have rejected the partition plan, fearing it would dilute their authority, especially over oil reserves in the Hadhramaut area. The Houthis say they want more rights for Zaidi Shia Muslims who are estimated to comprise around 40 percent of the population.

Neighboring Saudi Arabia backed southern separatists during Yemen’s 1994 civil war but it has also supported President Hadi.

The situation is further complicated by the presence of Al Qaeda in the Arabian Peninsula, which is seen as the most dangerous branch of the terrorist network, in central south Yemen. The United States regularly carry out airstrikes with unmanned drones against Al Qaeda members there. Hadi, a southerner himself, maintains that the Al Qaeda group coordinates its operations with the separatists. Separatist leaders deny any connection.