Dozens of Asian fisherman and their three vessels are being held hostage in Somalia by pirates who have demanded a $1.5 million ransom, officials said. The Taiwanese Foreign Affairs Ministry has said that the Somali gunmen threatened on Friday to start killing one hostage a day if the ransom was not paid within 48 hours. The hostages include three Taiwanese captains as well as 45 crew members from Indonesia, China, the Philippines and Vietnam. Gunmen have been holding the fishermen and their vessels near the southern Somali port of Kismayo since Aug. 15. They have demanded $500,000 for each of the boats and their crews, Taiwan's Foreign Affairs Ministry said. "Human right groups (and) civil society organizations are still engaged in negotiations with the hijackers to ensure the release of the hostages unharmed, by all means," Ali Bahsi, chairman of the Fanole Human Rights Center, a rights group in the Lower Juba region where the fisherman are being held, said Sunday.Bahsi said that he last talked to the kidnappers on Friday and they assured him then that the fishermen were safe. Taiwan has asked for international help in contacting the gunmen, and talked to the hostage-takers last week in an effort to negotiate a lower ransom. A ship carrying international food aid to Somali tsunami victims has been held by gunmen since late June.