The hugely controversial plans for a mass burning of copies of the Koran in the US have already prompted angry protests among Muslims.
In Kabul, several hundred Afghans, mostly pupils from religious schools, gathered outside a mosque, chanting “Death to America.”
Religious cleric Mohammad Mukhtar said: “It is the duty of Muslims to react. When their holy book, the Koran, gets burnt in public, then there is nothing left. If this happens, I think people’s first reaction will be to kill any Americans they come across.”
The Secretary General of the Arab League has denounced the plan as the work of a “fanatic”.
Meanwhile, Iran has warned if the protest goes ahead, the reaction will be “uncontrollable”.
Protesters also gathered in Indonesia, the world’s most populous Muslim nation.
This group in Jakarta urged the US government to step in to calm the brewing storm.