The Islamic State group is starting to attract the attention of radicals in Pakistan and Afghanistan, long a cradle for Islamist militancy, unnerving authorities who fear a potential violent contagion.

Far from the militants' self-proclaimed "caliphate" in Iraq and Syria, the name of IS has cropped up several times in jihadi circles in recent weeks in Pakistan and Afghanistan, the historic homeland of the Taliban and al-Qaida.

Leaflets calling for support for IS were seen in parts of northwest Pakistan, and at least five Pakistani Taliban commanders and three lesser figures from the Afghan Taliban have pledged their support.

Pro-IS slogans have appeared on walls in several cities in both countries and at Kabul University, where a number of students were arrested.

Militant, security and official sources say these are local, individual initiatives, and at this stage IS has not established a presence in the region.

Warning letter

But the success of IS in the Middle East is unsettling many of those charged with keeping a lid on Afghanistan's and Pakistan's myriad extremist groups.

"IS is becoming the major inspiration force for both violent and nonviolent religious groups in the region," Pakistani security analyst Amir Rana said.

Earlier this month, Pakistan's National Counter Terrorism Agency wrote to a dozen government agencies warning them to be on their guard against IS.

"The successes of IS play a very dangerous, inspirational role in Pakistan, where more than 200 organizations are operational," the agency said.

The letter came as the Pakistani army fights a major offensive against insurgent bastions in the tribal northwest, which appears to be weakening its major enemies, the Tehreek-e-Taliban Pakistan and allied al-Qaida fighters.

Following the army offensive, the TTP, a coalition of disparate militant groups, has fragmented into rival factions over recent weeks, fueling rumors the movement could be overtaken by IS.

The TTP says it broadly supports both IS and al-Qaida. It says it has sent 1,000 fighters in recent years to help jihadi fighters in Syria - an estimate confirmed by a Pakistani government source - and plans to send 700 more.

But if IS militants one day envisage extending their influence in Afghanistan and Pakistan, the world's only Islamic state with nuclear weapons, they will have to either defy or find an accommodation with the two countries' Taliban movements.

Currently, both the TTP and the Afghan Taliban officially recognize only one leader, Mullah Omar, and an Afghan commander said IS was wrong to declare a caliphate.

"The Taliban and their supporters say that 'amir-ul-momineen' (the commander of the faithful) has already been chosen," he said, rejecting IS leader Abu Bakr al-Baghdadi.

Money, money, money

So far the Taliban and al-Qaida's new South Asia wing have steered clear of criticizing IS, maintaining a united front against "Western aggression".

US officials say IS is generating tens of millions of dollars a month from black market oil sales, ransoms and extortion.

This financial heft is proving a big draw - including for the five Pakistani Taliban commanders who announced their support for IS.

A senior militant said, "The splinter groups are facing a financial crisis, so they are contacting Daesh." Daesh is another name for IS.

To spread in the region, IS must also eat away at the authority of the state - but, unlike Iraq and Syria, Pakistan's state structures look solid and are supported by a powerful army.

Afghanistan is much more fragile - particularly Kunar and Nuristan, mountainous provinces on the Pakistani border that have long been refuges for jihadi fighters from the hard line branch of Islam espoused by IS and al-Qaida.