A group of human-rights organizations is pressing WikiLeaks to do a better job of redacting names from thousands of war documents it is publishing, joining the list of critics that claim the Web site's actions could jeopardize the safety of Afghans who aided the U.S. military.

The letter from five human-rights groups sparked a tense exchange in which WikiLeaks founder Julian Assange issued a tart challenge for the organizations to help with the massive task of removing names from thousands of documents, according to several...