SANAA, April 20 (Reuters) - At least 78 people were killed in a stampede in the Yemeni capital Sanaa as hundreds gathered in a school to receive $9 per person in aid, the official media of the Houthi movement and witnesses said early on Thursday.

Al Masirah TV, the main television news outlet run by Yemen's Iran-aligned Houthi movement, said that in addition to the dead several people were injured including 13 who were in critical conditions, citing the director of health in Sanaa.

The stampede took place during the distribution of charitable donations by merchants in the final days of the Muslim holy month of Ramadan, the Houthi-controlled Ministry of Interior's spokesperson said in a statement.

Hundreds of people had crowded into a school to receive the donations, which amounted to 5,000 Yemeni riyals, or about $9 per person, two witnesses involved in the rescue effort told Reuters.

The interior ministry also said in a separate statement that the two merchants responsible for organising the donation event had been detained and an investigation was underway.

Yemen has been embroiled in an eight-year civil war which has killed tens of thousands of people, wrecked the economy and pushed millions into hunger.

A Saudi-led coalition intervened in Yemen in 2015 after the Houthis ousted the government from the capital Sanaa in 2014. The conflict has widely been seen as a proxy war between Saudi Arabia and Iran.

Riyadh and Tehran in March agreed to restore diplomatic ties severed in 2016 and prisoner exchanges this month between the two sides have raised hopes of a resolution to the conflict.

The top negotiator of Yemen's Houthi movement said recent peace talks with Saudi Arabia had made progress and further discussions would be held to iron out remaining differences.