"This is pure propaganda. This is not possible at all," Taliban spokesman Zabihullah Mujahid told AFP by telephone from an undisclosed location. He added that Omar was currently inside Afghanistan "leading the mujahideen".
The comments came after one Afghan intelligence source said Omar had been killed by Pakistan's ISI agency, while another claimed he had been missing for 11 days.
The first source, speaking to AFP on condition of anonymity, said that Omar had been killed on Friday, citing information received from sources within the Haqqani insurgent group, whose leaders are based in Pakistan.
"Based on ISI instruction through (former ISI chief) General Hamid Gul, Mullah Mohammad Omar was told to move from Quetta city of Pakistan to northern Waziristan," the source said.
"As Mullah Omar was being transported from Quetta to North Waziristan by the ISI, he was secretly killed by the ISI." However, a second Afghan intelligence source who also spoke anonymously said that Omar had been missing for 11 days following a meeting with Gul.
"It has been 11 days since his close circle, the people around him, have no clue of his whereabouts. The Taliban leadership are all concerned and worried for the sudden disappearence of Mullah Omar," the source said.
Afghanistan and Pakistan regularly trade accusations over Taliban insurgencies plaguing both their countries. There is deep distrust between Afghan intelligence and the ISI, which helped create the Taliban in the 1990s.