Younan Talia, of the Assyrian Democratic Organization, told The Associated Press that about 40 remaining Christian captives were released early Monday and are on their way to the northeastern town of Tal Tamr.
Younan said the release came after mediation led by a top Assyrian priest in northern Syria.
The extremists captured the Assyrians, members of an ancient Christian sect, last February after overrunning several communities on the southern bank of the Khabur River in northeastern Hassakeh province.
Kidnapping for ransom is a main source of income for the extremists. In November, ISIS said it killed a Norwegian and a Chinese captive after demanding ransom for their release two months earlier.
Talia said ISIS demanded a ransom of $18 million for the Assyrian Christians. He said the figure was later lowered following negotiations. He said he did not know the final amount.
Osama Edward, director of the Stockholm-based Assyrian Human Rights Network, said 42 Christians, mostly young women and children, were released. The Britain-based Syrian Observatory for Human Rights also said 42 were released, including at least 17 women.
A Syrian Christian figure said the worldwide Assyrian community launched a campaign for the captives’ release shortly after they were abducted. He said a bank account was opened in the northern Iraqi city of Irbil and donations began to flow in from around the world.
“We paid large amounts of money, millions of dollars, but not $18 million,” said the man, who requested anonymity because he was not authorized to discuss the sensitive mediation. “We paid less than half the amount.”
The official added that the fate of five Assyrians who went missing during the abductions was still unknown.
ISIS attacked a cluster of villages along the Khabur River, sending thousands of people fleeing to safer areas and capturing the Assyrians over a period of three days. Over the next two days, the extremists picked up dozens more from 11 communities near Tal Tamr.
The Hassakeh province, which borders Turkey and Iraq, has become the latest battleground in the fight against the ISIS group in Syria. It is predominantly Kurdish but also has Arabs, Assyrians and Armenians.
On Friday, the predominantly Kurdish Syria Democratic Forces captured the ISIS stronghold of Shaddadeh in Hassakeh, where some of the kidnapped were once believed to have been held.
Many Syrian Christians, who make up about 10 percent of Syria’s pre-war population of 23 million, left for Europe over the past 20 years, with the flight gathering speed since the country’s conflict began in March 2011.