Image caption Many of the Taliban's hardline views first materialised during resistance to the 1979 Soviet invasion

The last decade has seen a little-reported but systematic campaign by insurgents to silence Afghan clerics who disagree with their tactics and ideology.

More than 800 religious scholars who confronted the Taliban by calling their insurgency un-Islamic and unlawful have been killed.

The most recent killing took place a week ago when prominent religious scholar Maulawi Ata Muhammad was shot dead in Kandahar. He was head of programming for local radio station, Voice of Islam.

Some targets are very high profile. Among the first to be killed in this way was, Maulawi Abdullah Fayaz, head of the Kandahar religious scholars council, in May 2005.

The Taliban - a word which actually means religious student - have accepted responsibility for a number of these killings. Indeed, many of those killed either taught or influenced the men who went on to join the Taliban - in effect these students are now murdering their teachers.

The militants describe themselves as being at the vanguard defending Afghanistan's "original Islamic values". They accuse anti-Taliban clerics of justifying "foreign occupation and creating discord within the Muslim community".

No tolerance

My own records and other figures show that the majority of murders took place in the south of the country where the insurgency has been at its strongest and where a number of tribal elders and influential figures have been subjected to targeted killings.

Image caption Clerics wield enormous influence in Afghanistan and those who speak out against the Taliban are frequently targeted

Many of the dead were either prayer leaders in mosques or teachers at government schools. More than 50 were members or provincial heads of the pro-government National Council of Ulama (religious scholars or clergymen).

Their deaths have created a vacuum when it comes to religious knowledge and created a rift within the religious establishment, with profound implications for the future of healthy debate.

In traditional Afghan society religious scholars have a lot of influence - they usually use the prefix of Mullah, Maulawi or Maulana before their names.

Image caption The murders of so many clerics have left Afghan people in a religious vacuum

People in cities and villages respect them, seeking their opinion and advice on various matters and this is why they are useful for both sides in the Afghan conflict.

The National Council of Ulama was set up by the government in 2002 to challenge the Taliban's legitimacy as a religious movement.

The council also aims to enhance the government's religious credentials and so it publicly backs President Hamid Karzai's government and tries to influence decisions made by him.

The majority of the council's members are former mujahideen who fought against the Soviet invasion of Afghanistan in the 1980s. A few former Taliban members are also part of it.

About 3,000 religious scholars are formal members of the council which has issued religious edicts (or fatwas) justifying the presence of Nato forces under a UN mandate and calling on the Taliban to quit militancy and join the peace process.

They have also denounced the Taliban's call for a jihad, or holy war, against the Afghan government, arguing that it has been elected and that the president and other officials are Muslims.

'Support our struggle'

Image caption The Red Mosque in Kandahar where the head of Kandahar Ulama Council, Maulawi Hekmatullah Hekmat, was killed in a suicide attack in 2011.

In their edicts, pro-government religious scholars have also openly called the tactics used by the Taliban - especially suicide attacks and the random killings of civilians - un-Islamic.

"Many things are done in the name of religion which are not justified by religion, such as destroying and damaging mosques and schools," says Qazi Nisar Ahmad Siddiqui, head of the secretariat of the National Council of Ulama.

Hundreds of other pro-government clerics have received threats from the Taliban warning them that they too will be killed if they speak against the militants.

Several have had to leave their villages and towns fearing reprisals, especially those who have made overtly anti-Taliban speeches in mosques and on local radio.

The Taliban accuse these pro-government clerics of leading people astray and weakening "the strong morale of resistance fighters".

"If they deviate from the right path, they create a lot of problems," a Taliban commander told me some time ago.

"We want them to support our struggle."

The Taliban argue that the government is "illegitimate" because it relies on the support of "infidel powers" that toppled the government of the "Islamic Emirate of Afghanistan" - the name the Taliban use for their movement - in 2001.

"The Ulama working within Kabul's corrupt administration are viewed as criminals not as religious scholars," a Taliban spokesman said.

In some areas, the Taliban have even warned clerics not to offer prayers for dead members of the security forces.

Prominent murdered clerics 29 May 2005: Maulawi Abdullah Fayaz, head of the Kandahar Ulama (religious scholars') council, Kandahar Province

Maulawi Abdullah Fayaz, head of the Kandahar Ulama (religious scholars') council, Kandahar Province 17 Jul 2005: Maulawi Mohammad Saleh, head of Ulama council in Helmand province

Maulawi Mohammad Saleh, head of Ulama council in Helmand province 16 Oct 2005 : Maulawi Noor Ahmad Jan, head of the Ulama council of Kunar province

: Maulawi Noor Ahmad Jan, head of the Ulama council of Kunar province 08 Apr 2007: Maulawi Mohammad Anwar, head of the Ulama council of Khost province

Maulawi Mohammad Anwar, head of the Ulama council of Khost province 05 Jan 2011: Mullah Mohebullah Torpatkai, leading member of Ulama council, Helmand province

Mullah Mohebullah Torpatkai, leading member of Ulama council, Helmand province 13 Jul 2011: Maulawi Hekmatullah Hekmat, head of religious scholars' council, Kandahar province

Maulawi Hekmatullah Hekmat, head of religious scholars' council, Kandahar province 9 Oct 2012: Maulawi Abdul Samad, head of Ulama council of Uruzgan

Maulawi Abdul Samad, head of Ulama council of Uruzgan 11 Nov 2013: Maulawi Ata Muhammad, deputy head of clerics' council of Kandahar and head of programming at the Voice of Islam radio station

In one such incident in Kunar province in May 2013 a note left on the body of a local cleric read: "This will be the punishment of those who offer prayers for [dead] apostates."

Some of these hardline views first materialised during resistance to the 1979 Soviet invasion, an event which led to thousands of foreign fighters, mainly from the Middle East, introducing new ideologies and radical ideas to the region.

Dozens of moderate religious scholars have also been killed in Pakistan by their own "neo-Taliban" students who have adopted a similarly radical ideology.

Two well-known examples are the murders of leading Peshawar-based Sunni cleric Maulana Hassan Jan in 2007 and religious scholar Sarfraz Naeemi in 2009 in Lahore. Both men were strongly critical of suicide bombings.

Another prominent religious scholar, Muhammad Farooq Khan, was killed in October 2010 by the Pakistani Taliban in Swat who said that he was "involved in propaganda against the Taliban".

A number of clerics in Afghanistan have chosen not to take sides by avoiding any discussion of sensitive issues such as Nato's presence in the country and the tactics used by the Taliban. They fear a Taliban reaction or - at the other end of the scale - arrest by the security forces.

These killings bear witness to the explosive clash between those clerics who are part of the Taliban and those who criticise insurgency - and there is no sign this confrontation is going to die down.

By silencing the moderate clerics, insurgents are posing serious challenges to the stability of both Afghanistan and Pakistan.