ADDIS ABABA - An Iranian man held by Somali pirates for more than four years was flown to Ethiopia's capital Saturday after his captors released him because he needed urgent medical care.

The release of Mohammad Shariff Panahandeh means just three hostages remain in the custody of Somali pirates, according to the Hostage Support Partnership, the charity that negotiated his release.

His health had deteriorated significantly in recent weeks, lending new urgency to efforts to secure his freedom, John Steed of the Hostage Support Partnership told AFP on Saturday.

"He's severely malnourished. He lost a huge amount of weight. It reminded me of someone who's just been released from Belsen [a Nazi] concentration camp," Steed said.

Shariff is also suffering from "severe stomach problems and internal bleeding," Steed said.

Shariff arrived in Addis Ababa on an Ethiopian Airlines flight from the city of Garowe. He will receive some medical care in Ethiopia before being flown home to Iran, Steed said.

Shariff was captured with three other men in March 2015 after an attack on the Iranian fishing vessel FV Siraj.

Officials with the Iranian embassy in Addis Ababa could not be reached for comment Saturday.

Steed said no ransom was paid for Shariff, but that the pirates were likely to try to hold out for large sums before letting the other three go.

In a statement announcing Shariff's release, the Hostage Support Partnership said Somali community leaders had been crucial in the negotiations.

Steed said the same kind of local involvement would likely be needed in the case of the final three hostages.

"We need to get them out," he said.

Pirate attacks on maritime vessels off the Somali coast peaked at 176 in 2011 before falling off sharply in recent years.