Taliban chiefs have urged "Islamic State" (IS) jihadis not to wage a parallel insurgency in Afghanistan. Their letter to IS leader Abu Bakr al-Baghdadi follows reports that several Afghan groups have switched sides.
The Taliban has warned the leader of the IS militant organization to stay out of Afghanistan after a wave of defections to its jihadi rival in recent months.
In a letter to IS leader Abu Bakr al-Baghdadi, the Taliban warned it "didn't want to see interference in its affairs" and would be "forced to react" if the militants, who have swept through large parts of Iraq and Syria over the past year, operated officially inside Afghanistan.
In recent months, the country has seen an upsurge in violence from militants associating themselves with IS, including a suicide bombing in Jalalabad in April which killed 35 people.
American military officials claimed last month that IS had been actively recruiting fighters in Afghanistan, although they were not fully operational.
Over the last week, pitched battles took place between the Taliban and supporters of IS in eastern Afghanistan, with as many as 25 deaths reported on both sides and dozens of casualties.
Reports suggest a growing disquiet within the Taliban with many rebels replacing white Taliban flags with the black flags of the upstart insurgents who are seen by many as a more lethal force.
But Tuesday's letter insisted that the holy war against the Americans and their allies must be conducted "under one flag, one leadership and one command."
Some analysts think the Taliban's backers are frustrated with the group's inability to gain substantial territory, despite the withdrawal of NATO troops from Afghanistan at the end of last year.
Written in several languages - Dari, Pashto and Urdu as well as Arabic - the note appeared intended to dissuade other Taliban fighters from switching sides.
"The Taliban are like an expired formula. They know this and increasingly fear being sidelined," Kabul-based author and analyst Ahmad Saeedi told the AFP news agency.
Saeedi also sees the letter as an olive branch to Islamic State and a clear warning that they should not fight each other.
Concerns about IS's arrival in Afghanistan could help to progress peace negotiations between the Taliban and the Afghan government. Reports suggest Taliban officials have displayed a new willingness to participate.
Preliminary talks continue in Oslo on Tuesday ahead of possible face-to-face meetings in the future.
The Taliban ruled Afghanistan for five years from September 1996 under a strict interpretation of Sharia law before being topped by the US-led invasion in 2001.
mm/rc (AFP, Reuters)