The mounting persecution of Christians around the world has reached such a point that Pope Francis and other religious liberty advocates have already described the problem as a form of "genocide" affecting some 200 million Christians in more than 60 countries.

In his visit to Bolivia during his recent trip to Latin America, the Pope said he was disturbed by the rising cases of Christians getting killed for their faith, The Guardian wrote.

"Today we are dismayed to see how in the Middle East and elsewhere in the world many of our brothers and sisters are persecuted, tortured and killed for their faith in Jesus," Pope Francis said.

The leader of the 1.2-billion-strong Roman Catholic Church demanded an end to the genocide.

"In this Third World War, waged piecemeal, which we are now experiencing, a form of genocide is taking place, and it must end," Pope Francis said.

John Pontifex of Aid to the Church in Need, which monitors cases of persecution, said there is "a form of religious-ethnic cleansing of Christian communities."

"The persecution of Christians is at a level we've not seen for many, many years and the main impact is the migration of Christian people. There are huge swaths of the world which are now experiencing a very sharp decline in the number of Christians," Pontifex said.

While Prince Charles of UK called the threats to Christians in the Middle East "an indescribable tragedy," David Alton, a cross-bench peer at the House of Lords, said the number of persecuted Christians is enormous, noting that "some assessments claim that as many as 200 million Christians in over 60 countries around the world face some degree of restriction, discrimination or outright persecution."

"Whatever the real figures, the scale is enormous. From Syria, Iraq, Iran and Egypt to North Korea, China, Vietnam and Laos, from India, Pakistan, Bangladesh and Sri Lanka to Indonesia, Malaysia, Burma, from Cuba, Colombia and Mexico to Eritrea, Nigeria and Sudan, Christians face serious violations of religious freedom," he said.

The cases of persecution in the past 15 months include the taking of more than 270 Nigerian schoolgirls, the execution of 21 Egyptian Coptic Christians in Libya, and the killing of 147 people in a university in Northern Kenya.

The Pew Research Center reported in March that Christians face persecution in 102 countries around the world.

Lisa Pearce of Open Doors, a religious liberty monitoring group, told The Guardian that the organisation is struggling with how to "make clear [that] we're talking about the impact of extremism, that it's not only Christians that are persecuted, and that the overall goal is to create an environment where people are free to follow any religion, or none."

Pearce said "this is not an issue just for Christians, but a human rights issue that affects us all. It's not a problem for the church, but much wider than that."

Christians suffer harassment in 102 countries more than any other religion, according to the Pew Research Center.