In a statement posted in English on a Taliban website, marking the end of the Muslim fasting month of Ramadan and attributed to the reclusive Taliban leader, Omar said US and British offensives in recent months had been a failure.
"The Islamic Emirate of Afghanistan calls on the public of the West not to be deceived by the assertions of Obama, who says the war in Afghanistan, is a war of necessity. The West does not have to wage this war," the statement said.
"The public of the West should also not be deceived by the assertions of the general secretary of NATO and British Prime Minister who claim the war in Afghanistan is for the defence of the West. Such deceiving and baseless utterances must not confuse you."
A Taliban spokesman, Qari Yousuf, said the statement was genuine. The precise whereabouts and health status of Omar are not known, as he does not appear in public.
Obama, who has already ordered 21,000 extra troops to Afghanistan this year, is expected to consider a request for more troops from his commander there in coming weeks.
There are now more than 100,000 Western troops in Afghanistan, two thirds of them Americans.
"The invaders should study the history of Afghanistan from the time of the aggression of the Alexander," the statement said.
"Still, if they are bent on ignoring the history, then they themselves saw with their own eyes the events of the past eight years. Have they achieved anything in the past eight years?"
US commanders believe the reclusive Taliban leader has been hiding in Pakistan since he was driven from power in Kabul in 2001 after refusing to turn over al Qaeda leader Osama bin Laden after the September 11 attacks on the United States.
A press officer for US and NATO-led troops in Afghanistan, Captain Elizabeth Mathias, declined to comment on the statement.
Kabul: Afghan Taliban leader Mullah Omar issued a statement on Saturday telling people of the West not to listen to US President Barack Obama's justifications of war and vowing to defeat NATO troops like other invaders of history.
First Published: Saturday, September 19, 2009, 21:18