ISIS today released the last of some 230 Assyrian Christians kidnapped a year ago in Syria after receiving millions of dollars in ransom, Christian officials said.

Younan Talia, of the Assyrian Democratic Organisation, said about 40 remaining Christian captives were released early today 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.

Free: The first freed members of Christian Assyrian community embrace their relatives after being released by ISIS in March last year. The terror group released the last 40 of the 230 Assyrian Christians kidnapped a year ago in Syria after the receiving millions of dollars in ransom

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 $18million 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.

At the time, it was not clear why ISIS freed these captives while keeping more than 200 others. All have now been freed after the worldwide Assyrian community launched a campaign to free the captives

'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.

IS 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 Islamic State group in Syria. It is predominantly Kurdish but also has Arabs, Assyrians and Armenians.

On Friday, the predominantly Kurdish Syria Democratic Forces captured the IS stronghold of Shaddadeh in Hassakeh, where some of the kidnapped were once believed to have been held.