Walter Kaelin, a special representative of UN Secretary-General Ban Ki-moon, said tens of thousands of Afghans have already been driven from their homes in 2007 alone.
He also urged foreign and Afghan government forces fighting Taliban insurgents to do more to avoid civilian casualties.
Kaelin made his remarks in a report issued today after a visit to Afghanistan. The report urged all sides in the fighting "to distinguish at all times between civilians and combatants" in a way that "avoids disproportionate impacts causing civilian death."
The report also condemns what Kaelin called "the systematic disregard of international humanitarian law by the Taliban."