Islamic State militants kidnapped 90 Christians in north-east Syria as the jihadis retreated in the face of a Kurdish counter-offensive, a monitoring group has said. The reported kidnappings are the latest blow to the ancient Christian presence in the region, heightening insecurity after a video was released by militants claiming allegiance to Isis that appeared to show the beheading of 21 Egyptian Copts in Libya. Syria conflict four years on: share your stories Read more "This is another episode in the targeting to the Christians of the east," Habib Afram, president of the Syriac League in Lebanon, which represents the Assyrian minority, told the Guardian. "We are witnessing the end of the Christian presence in the east." The Syrian Observatory for Human Rights (SOHR) said 90 Assyrian Christians were kidnapped by Isis near Tal Tamr. In addition to the captives, four Christians were killed trying to defend the villages. The attack targeted some 35 mostly Assyrian settlements near the Khabur river, a tributary of the Euphrates, after there had been heavy fighting in the area between Isis and the YPG, the Kurdish militia backed by the US-led coalition that beat back an advance on the border town of Kobani last month. The rights monitoring group said its sources on the ground had overheard Isis militants on radios refer to the captives as "crusaders", the same term used by militants to describe the Egyptian Copts apparently killed in Libya. Afram said the Kurds had reported that churches in the area had been burned and that the militant group may be seeking a prisoner swap with the Kurdish forces. The attack is symbolically significant because the Assyrian Christians had fled to the region in 1933, taking refuge after the infamous Simele massacre, a pogrom by the Iraqi kingdom at the time targeting the population. It also comes close to the centenary of the massacres against Armenian and Assyrian Christians under the Ottoman empire. "The Assyrian people are not merely Christians, but indigenous inhabitants of the Middle East," said Mardean Isaac, an Assyrian writer based in the UK and member of A Demand for Action, an organisation dedicated to supporting the Assyrians and other minorities in Iraq and Syria. "After the Iraq war of 2003, and since the Syrian crisis began, the persecution unleashed on them -- including extortion, kidnappings, murder, the ethnic cleansing of entire swaths of Baghdad, the Nineveh plains, and now much of north-east Syria, has been so vast that their very existence in their ancestral homelands is in grave peril. "We are watching a living history and all that comprises [it] disappear," he added. Isis militants have often singled out Christians and minorities for persecution. Thousands of Christians fled Iraq's Mosul and Nineveh after Isis's lightning advance last summer amid reports of forced conversions. Many took refuge in Kurdish-held territories or in Lebanon. The Isis rampage through Iraq's Nineveh plains forced out Chaldean Christians and other minorities from areas in which they had co-existed for nearly 2,000 years. The jihadis have been especially brutal towards the ancient Yazidi minority in Iraq, attempting to starve thousands who were stranded on Mount Sinjar, north-west of Mosul. It also sold many hundreds of Yazidi women into slavery and forced others to marry. Coalition air strikes had earlier targeted Isis fighters near the Syrian Kurdish stronghold of Qamishli on the Turkish border. Afram, who said he was in contact with the Syrian Orthodox bishop of Hassakeh, the Syrian Kurdish stronghold not far from the villages, described the kidnappings as part of a series of attacks targeting Christian communities across the region, including attacks in Baghdad and Mosul, the slaying of the Egyptian Copts, and the occupation of the ancient Christian town of Maaloula by Jabhat al-Nusra, the al-Qaida affiliate in Syria, and the eviction of Christians from their homelands in Nineveh. Afram said many had fled to Hassakeh to take refuge, creating a humanitarian crisis amid shock at the attack. "They are not part of the struggle," he said, saying the Christians in the area had not been involved in any military operations. "We do not understand this targeting of Christians." Afram also condemned the "frightening and shocking Arab silence" at the ongoing attacks against the Christians in the region, saying there was no plan to confront the crisis and that air strikes would not stem the tide of terrorism against the region's minorities. "Coexistence needs two sides," he said. Archbishop Paul Nabil El-Sayah, vicar general of the Maronite patriarchate in Lebanon and curial bishop of Antioch, said Isis was targeting all those who did not believe in its ideology. "They do not want to coexist with either Christians or Muslims who do not believe in their mission," he told the Guardian. Sayah said those who armed extremist groups in the region and provided them with support were also to blame for such attacks. "Those who kidnap are criminals, but those who are supporting them are the real criminals," he said. As well as many Assyrians, thousands of Iraqi Chaldeans have also fled to Lebanon since Isis took control of Mosul in a lightning offensive last summer. The majority of Iraq's Christians are part of the Chaldean church. More than 1,600 people, the vast majority of them from Isis, have been killed by the US-led coalition air strikes in Syria, according to SOHR. Many of the jihadi casualties occurred in the Kurdish town of Kobani, on the Turkish border, where Isis has estimated its losses to be at least 1,400.