Yemenis who were airlifted to Jordan to undergo treatment for critical illnesses earlier this year were brought home on Sunday on a flight into the rebel-held capital Sanaa, the United Nations said.

Thirty-one men, women and children in dire need of medical care were flown out in February along with their companions.

"A U.N. flight carrying civilian Yemenis & their companions just landed in #Sanaa," the United Nations Office for the Coordination of Humanitarian Affairs said in a tweet, without saying how many had returned.

"Thanks to the U.N. medical air bridge, the patients received treatment in #Jordan for different chronic conditions for which they could not be treated inside #Yemen."

The U.N. organized two evacuation flights to Amman in February, the first carrying seven children and the second with 24 other patients.

"Nine patients and their companions arrived in Sanaa on board the U.N. chartered plane," Dr Motahar Darouiche, head of the airlift on the side of the Huthi rebels who control Sanaa and much of northern Yemen, told reporters. 

He said 10 Yemeni patients were still in Jordan. 

"Five will return on Monday and the other five after the repatriation procedures are completed," he added. He did not specify where the remaining patients were.

Darouiche called for the reopening of Sanaa airport to commercial flights to "alleviate the suffering of thousands of patients who need treatment abroad." 

The military coalition led by Saudi Arabia, which backs Yemen's internationally recognized government, imposes an air blockade on the Huthis, which has resulted in the closure of Sanaa airport to commercial flights since 2016. 

Last November the coalition said it was prepared to allow medical evacuations from the airport as a confidence-building measure to support U.N. peace efforts.

The return of the medical flight comes shortly after the warring sides in Yemen's long conflict agreed to exchange 1,081 prisoners, after talks in Switzerland.

The release of the loyalists and insurgents -- if it materializes -- would mark the first large-scale handover since the war erupted in 2014.

The agreement was a modest step forward amid efforts to end he six-year conflict that has killed tens of thousands of people, mostly civilians, and led to what the U.N. describes as the world's worst humanitarian crisis.