SANAA, Yemen (AP) — The first direct flight from Iran to Yemen's capital arrived on Sunday, as the Shiite rebels holding Sanaa formalize ties with the regional Shiite powerhouse.

The flight underscores how the rebels, known as Houthis, are strengthening their grip over state institutions and exercising sovereign power in Sanaa, even as the country's president insists he is still in charge after fleeing to the south.

Yemeni airport, security and transportation officials greeted the Mahan Air flight, an Airbus 310 carrying Iranians including aid workers from the Iranian Red Crescent.

Iran's deputy ambassador, Rasai Ebadi, told The Associated Press that the plane carried humanitarian aid including tents and 12 tons of medicine, adding that more aid would come soon.

The rebels signed an agreement with Iranian authorities in Tehran on Saturday to establish 14 direct flights per week between the two countries.

The rebels, who overran Sanaa last September, are widely believed to have support from Iran, a claim they frequently denied. Yemeni President Abed Rabbo Mansour Hadi has established a base in the southern city of Aden, from where he says he is still the country's rightful ruler.

Over the past days, Gulf countries have moved to support Hadi's claim of legitimacy, with Bahrain, Saudi Arabia, the United Arab Emirates and Kuwait moving their embassies to Aden.