A new campaign to help besieged Christians in Syria and Iraq has been launched by Aid to the Church in Need, by the US branch of the papal agency, Aid to the Church in Need, which warned that both countries faced extinction of their ancient Christian communities.

The $1 million campaign is a response to what Patriarch Louis Raphael I Sako, Iraq's Chaldean Catholic leader, called "a human catastrophe and the risk of a real genocide."

Two grants have already been made, of $186,000 in support of the Christian community in Syria and $135,000 for emergency aid for Iraq's Christian refugees.

Continued fighting between the regime and the opposition, the devastation caused by the civil war to-date and targeted attacks are causing enormous suffering to local Christians in Syria, the charity said.

George Marlin, chairman of Aid to the Church in Need, said: "Both countries are threatened with the extinction of ancient Christian communities. Both Churches and governments in the West must do their utmost to prevent what has become a tragedy of historic proportions."

He called on the West to intervene to stop the atrocities of the Islamic State in Iraq, which have been marked by "cruelties beyond words." There have been reports of beheadings and crucifixions of Christians and other minorities. Water, food, emergency supplies and medicine "are the first order of the day," he said.

The Syrian conflict has sparked the exodus of almost a third of the country's Christian population of 1.8 million, most stranded in Lebanon. In Iraq, the Christian population has fallen to about 150,000 from a high of more than a million.

In Syria, the charity will be supporting the Archdiocese of Homs, Hama and Yabroud and provide emergency relief for families in the country's famous Valley of the Christians, which has seen some of the most intense fighting of the Syrian civil war.

"Not only is the rich Christian patrimony of these countries at stake," said Marlin. "Christians play a vital role in Muslim societies as a moderating force, playing an indispensable role in mediating between warring factions and maintaining relations with the international community."

The commitment of the Christians in the Middle East to "education and democratic values across the board" makes them peace-builders, he said—and that is a "vital interest for the West."

Christian Aid, which launched its Syria Crisis Appeal last year, said most of the refugees, many of them highly qualified doctors, teachers and other professionals, wanted to return with their families to Syria.

Lucy Batchelor, Christian Aid's emergency programme manager for Syria, said the situation was of "quite significant desperation". Three years after the conflict in Syria began, more than 150,000 people have been killed, 2.8 million refugees have fled to neighbouring countries and another 6.5 million people have been displaced inside Syria.

In its latest annual report on religious freedom, published at the end of July, the United States said that in Syria, as in much of the Middle East, the Christian presence is becoming a shadow of its former self.

"After three years of civil war, hundreds of thousands fled the country desperate to escape the ongoing violence perpetrated by the government and extremist groups alike. In the city of Homs the number of Christians dwindled to as few as 1,000 from approximately 160,000 prior to the conflict," the report said.

"In Syria, the Assad regime increasingly characterised the conflict in sectarian terms and targeted religious groups it considered opposition-aligned, particularly members of the country's Sunni majority. Regime-aligned militia groups composed of Iraqi Shia and Hezbollah fighters targeted members of groups seen as aligned with the opposition, especially Sunnis. Militant groups, especially those linked to al-Qa'ida, increased their targeting of Alawite, Shia Muslim, Christian, and other religious communities, some because of perceived alignment with the regime. Many Syrian Christians have fled the country as a result," the report added.

The Archbishop of Canterbury Justin Welby, preaching at the Holy Sepulchre Maori Mission Church in Auckland, New Zealand, on Thursday called for action "to serve, to transform."

He said: "This evening, the appalling events of Iraq, and equally terrible killings in Northern Nigeria and in Syria, the war in the Ukraine, and in so many other parts of the world. The seeming endless repetition of the terrible tragedies of Gaza and of the whole of Israel and Palestine. All these events and movements propel us towards fear, and fear takes us to self-protection, and self-protection drives us to action that only makes things worse.

"There must of course be actions. We are an active people. Christians are called by God to serve, to transform. Yet the pattern of action is set by the figure on the Cross."