Shocking accounts of medieval brutality — including video of kneeling Iraqis being gunned down, a Twitter image of a young jihadist holding a severed head and threats by ISIS to take its savagery to the White House — have prompted desperate calls for the international community to stop the fanatical Islamic group.

UN Secretary General Ban Ki-moon this week joined Pope Francis, Egypt's top cleric and several world leaders in condemning the terrorist group, which now calls itself Islamic State and has carved out a caliphate, or nation of strict Sharia law, in northern Iraq and Syria.

"I am profoundly dismayed by its barbaric acts, including accounts of summary executions, boys forcibly taken from their homes to fight, girls abducted or trafficked as sex slaves," Moon said Tuesday. "I urge the international community to do even more to provide the protection they need. And I condemn in the strongest possible terms the systematic persecution of individuals from minority populations and those who refuse the extremist ideology of 'IS' and associated armed groups."

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Pope Francis condemned the terrorist group in St Peter’s Square on Sunday, saying that the violence against Christians and other minorities "seriously offends God and seriously offends humanity." The Vatican sent the Pope's personal envoy to Iraq on Tuesday to help persecuted Christians. At least one top Muslim leader, Egypt's Grand Mufti Shawqi Allam, also expressed outrage at the terrorist group's barbarism and said their actions are a "danger to Islam."

A list of heinous acts attributed to ISIS include mass executions of Iraqis, severed heads affixed to poles in conquered towns and an endless stream of photos and video put out on the Internet showing killers grinning next to their innocent victims.

Canon Andrew White, the vicar of the Anglican Church in Baghdad, said a five-year-old Christian boy was "cut in half" by ISIS fighters, in an account shocking even by ISIS standards. White, who heads St. George's Church, in the heart of Baghdad, said the boy -- named "Andrew" after White, who baptized him -- was killed when ISIS stormed the Christian town of Qaraqosh in northern Iraq.

"I’m almost in tears because I've just had somebody in my room whose little child was cut in half," White told the Anglican News Service. "I baptized his child in my church in Baghdad. This little boy, they named him after me – he was called Andrew.'"

When reached by phone Wednesday, White confirmed the atrocities being committed against Iraqi Christians by ISIS and also criticized the media for its "irresponsibility" in failing to adequately cover the violence against religious minorities.

"Our people have been killed, massacred," White told FoxNews.com. "It's horrendous."

He said ISIS is targeting all Christians in the northern regions of the country, executing Iraqis who do not adhere to the terrorist group's version of Sunni Islam.

"They've even gouged out people eyes and said they belong to us," White said. He declined to comment further on the boy, saying, "It's too painful for me to talk about."

Of those families who have managed to be spared, White said, "They have lost everything -- all their money and all their gold."

Australia was recently sickened when one if its own became an ISIS jihadist, traveled to Syria and then posted a photo on Twitter of his son holding a severed head with the inscription: "That's my boy!"

“(The) Islamic State — as they're now calling themselves — it’s not just a terrorist group, it’s a terrorist army and they’re seeking not just a terrorist enclave but effectively a terrorist state, a terrorist nation," said Prime Minister Tony Abbott. “This does pose extraordinary problems — extraordinary problems, not just for the people of the Middle East, but for the wider world and we see more and more evidence of just how barbaric this particular entity is.”

The United Nations could not independently verify the alleged killing of children, but continues to investigate such reports, a UN spokesman told FoxNews.com. Terror experts say the danger within the region makes it difficult for the UN and others to confirm some of the reports, but also note that in many instances no verification is needed when the terror group posts graphic photos and claims responsibility for the atrocities.

"The Islamic State clearly has genocidal ambitions and they're creating all sorts of war crimes so nothing would surprise me," Thomas Joscelyn, a senior fellow at the Foundation for Defense of Democracies, told FoxNews.com.

"A war zone makes it very difficult to verify specific atrocities" and "there is some misinformation out there," he said, but added, "Some [reports] don't require verification because the group is claiming responsibility. They post their own war crimes to the Internet."

"The scale of this is something we haven't witnessed in a long time," Joscelyn said of the bloodshed.

Munir Salim Kakish, chairman of the Council of Local Evangelical Churches in the Holy Land, said he has little doubt ISIS is killing Christian children in Iraq.

"They have been hanging children and also putting their heads on posts," said Kakish, who is based in Ramallah and Ramla. "There is nothing this group won't do. They are a barbaric people."

"We have to move fast and with much more power," he said of the U.S. involvement in the region. "Their goal is to wipe out all Christians – approximately 13 million in the Middle East – and that includes children."

"When they finish with Syria and Iraq, they’ll move to Jordan and Lebanon and Palestine and Saudi Arabia," he told FoxNews.com.

The targeting of Iraqi Christians began in July in Mosul -- the northern city where Christians have lived and worshiped for 2,000 years -- when non-Muslims were purged by the jihadist terror group that claims to have established its own nation in the region.

So far, the U.S. has mounted air strikes on ISIS positions and dropped food and other humanitarian aid to religious minorities seeking refuge from ISIS. The United Kingdom has joined in the aid drops, but Prime Minister David Cameron is under increasing pressure at home to join in the strikes as Iraq's army and the Kurdish Peshmerga fighters battle the ISIS army, estimated at about 10,000.