The Islamic Movement of Uzbekistan (IMU) has accused the Taliban of deceit and collusion, and demanded that the Afghan militant movement tell the truth about the circumstances of its late leader's death.
The comments were made in an August 2 statement addressed to the Afghan Taliban and received by RFE/RL's Uzbek Service by e-mail on August 4. The e-mail was sent from an address established as belonging to an IMU source.
Referring to the Taliban as the "Islamic Emirate of Afghanistan" -- the name of the unrecognized state ruled by the Taliban regime from 1996 to 2001 -- the statement openly questions the details surrounding the Taliban's confirmation of the death of Mullah Mohammad Omar.
Afghan officials announced on July 29 that the longtime Taliban leader died in a hospital in the Pakistani city of Karachi in April 2013 while undergoing treatment for an unspecified illness.
Taliban spokesman Zabihullah Mujahid confirmed the next day that Mullah Omar had died of an unspecified illness, but without saying when or where and also adding that Omar had not left Afghanistan since 2001.
In the statement obtained by RFE/RL's Uzbek Service, the IMU said that the Taliban's explanation of Mullah Omar's death "cannot be trusted," and accused the Afghan militant group of collaboration with Pakistan's spy agency, the Directorate for Inter-Services Intelligence (ISI).
"For 14 years, lies about our beloved commander Mullah Mohammad Omar's life and death have been given to the community of Islam, and the latest statements about the circumstances of his death are continuation of such lies," the statement says.
The IMU statement specifically questioned claims that Mullah Omar died after two weeks of hospitalization, and demanded full and detailed explanations of the circumstances of his death. The IMU expressed the hope that "all our requests will be fully met."
The IMU, which is active in Afghanistan and Pakistan, is on the U.S. State Department's list of foreign terrorist organizations and is banned in Central Asian countries and Russia. It is known to have links with Al-Qaeda and Taliban militants, but earlier this year vowed its allegiance to the Islamic State (IS) group.
The Taliban has publicly condemned IS for waging a parallel insurgency in Afghanistan.
In a letter addressed to IS leader Abu Bakr al-Baghdadi in June, the Taliban insisted that "jihad [holy war] against the Americans and their allies must be conducted under one flag and one leadership."
"The Islamic Emirate [Taliban] does not consider the multiplicity of jihadi ranks beneficial either for jihad or for Muslims," said the letter signed by then-Taliban deputy leader Mullah Akhtar Mohammad Mansur.
"Your decisions made from a distance will result in [IS] losing support of religious scholars, mujahedin...and in order to defend its achievements the Islamic Emirate will be forced to react," it added.
The letter, published on the Taliban's website in Pashto, Urdu, Arabic, and Dari, did not elaborate on its threat.