A direct flight from Tehran arrived on Sunday to Yemeni capital Sanaa, the first by Iranian airlines since the unification of Yemen in 1990.
"An Iranian flight carrying a medical aid consignment arrived today in Sanaa International Airport from Tehran," Mohamed al-Serihi, senior official at Sanaa airport, told The Anadolu Agency.
Senior Iranian diplomats were on hand to welcome the flight -- the first between the two countries in many years.
Yemen's official Saba news agency, which is controlled by the Shiite militiamen who overran Sanaa in September, said that under the deal Iran Mahan Air and Yemenia would operate 14 flights each a week.
Western-backed President Abedrabbo Mansour Hadi, who fled last weekend an effective house arrest by the Houthis in Sanaa, slammed the agreement as "illegal," according to an aide.
"Those who signed it will be held accountable," Hadi said during a meeting with tribal chiefs in the southern city of Aden where he is now based.
Tehran has repeatedly been accused of backing the Huthi militia.
US Secretary of State John Kerry said on Tuesday that "critical" support of the militia by Shiite-dominated Iran "contributed" to the collapse of Yemen's government.
Iran rejected Kerry's "blame game," insisting that foreign intervention in Yemen would "further complicate the situation."
The semi-official Iranian news agency Fars had said that direct flights between Sanaa and Tehran would open the door for the export of Iranian commodities to Yemen.
Tension has mounted in Yemen since the Houthi group seized control of Sanaa in September 2014. The group has sought to extend its control in other Yemeni provinces since.
On 6 February, the Houthis issued what it described as a constitutional declaration dissolving Yemen's parliament and establishing a 551-member transitional council.
The declaration was, however, rejected by most of Yemen's political forces – along with some neighboring Gulf countries – which described it as a coup against constitutional legitimacy.