An Iranian sailor that had been held hostage by Somali pirates for three and a half years has finally been freed, a former British army officer who helped negotiate for his release said on Sunday.

Mohammad Sharif Panahandeh was among 21 crew members aboard a boat that was hijacked in March 2015. Eight of the hostages died, five escaped, and Iran freed four last year. Three still remain in captivity.

"This guy was dying – he looked like a skeleton. He was bleeding internally. He had severe malnutrition. I suspect the others are in a similar condition," Reuters quotes John Steed, a retired British colonel. Steed has worked in the region for many years trying to free Somali hostages.

Steed said the hostages had been split up by their captors after arguments over money. Panahandeh was released because his captors thought he would die.

“He was released last weekend but we had him in (the northern Somali town of) Galkayo trying to get him fit to travel. A week of trying to get him fit to travel. We had to stabilize him,” Steed said.

Steed added that the captives could not get anyone to pay the ransom demanded because they were from poor backgrounds.

Iran’s Foreign Ministry spokesman Abbas Mousavi said on Saturday that the United Nations and Steed’s humanitarian group, the Hostage Support Partnership, helped with the release.

"We are happy to announce we have obtained the release of one of the last hostages of Somali piracy … 3 more seafarers remain who need our help," Hostage Support Partnership tweeted.

Somalia witnessed a hike in piracy off its waters in 2012, but the cases dropped later as shipping companies enhanced security on their vessels. Others resorted to sailing further away from Somalia.