The UN launched the three-day vaccination campaign in six Afghan provinces on its Peace Day, September 21, with an aim to immunise 1.85 million children under five against the crippling disease.
But "regrettably 190,000 children, most of them in districts of (southern) Helmand and Kandahar (provinces), could not be reached because of obstruction or fighting," UN spokesman Jamil Danish told reporters.
This was despite pledges from the Taliban, responsible for much of the violence in those areas, to not attack or hinder the thousands of vaccinators, most of them volunteers or health workers.
International and Afghan forces had also agreed to hold fire on Peace Day and afterwards accused the Taliban of carrying out several attacks.
Afghanistan is one of a handful of countries that still has the crippling polio virus, with 18 new cases reported this year, all in the south and east where insurgent violence is the strongest and health workers most at risk.
The UN again called on Afghans to leave health workers out of their disputes for another nation-wide polio vaccination campaign due next month.