Mullah Mohammed Amin said resurgent militants had built up stockpiles of weapons and were bent on vengeance against "the foreign invaders".
The Taliban, overthrown by the invasion, now wanted to export terror to the West, he said.
"It's acceptable to kill ordinary people in Europe because these are the people who have voted in the government," he said.
"They came to our home and attacked our women and children," he added. "The ordinary people of these countries are behind this -- so we will not spare them. We will kill them and laugh over them like they are killing us and laughing at us."
Amin said the Taliban was inspired by tactics used by insurgents in Iraq, namely remote-controlled bombs, land mines and suicide bombers.
"They are our best tactic," he said.
Fighters were sheltering in Pakistan and being aided by sympathetic locals, he said in an interview with the British TV channel in the Pakistani border region.
NATO Secretary General Jaap de Hoop Scheffer said on Thursday that suicide bomber tactics proved that Taliban rebels could not defeat multinational forces through conventional warfare.
"The Taliban and the other spoilers of the process of nation-building and democracy in Afghanistan are having to go with these kinds of horrible tactics -- improvised explosive devices, suicide bombers and so on -- because they know they cannot beat NATO in other ways," he told BBC radio.
There are around 31,000 NATO-led International Security Assistance Force soldiers in Afghanistan trying to help the government establish stability against a resurgent Taliban to allow reconstruction.
Some of the 37 nations in the force have admitted to facing some of their fiercest fighting in decades.
Led by Mullah Mohammed Omar, the Taliban's movement effectively ruled most of Afghanistan from 1996 until 2001.
They sheltered Osama bin Laden's al Qaeda terror network, which was responsible for the deadly September 11, 2001 attacks on the United States.

Copyright AFP (Agence France-Presse), 2006