Of those, the report said, 77 percent were caused by the Taliban and other insurgent groups, an increase over 2010 despite the Taliban's pledges to strive to stop killing civilians, The New York Times reported.
The number of civilians killed by pro-government forces, including NATO troops, dropped to 410, or 14 percent of those killed, while in 9 percent of the deaths, the party responsible wasn't clear.
The annual U.N. report, in its fifth year, tracks deaths of all non-combatants based on U.N reporting and investigations.
The number of civilians killed rose 8 percent over 2010, but the increase in each of the past five years shows that even amid talk of peace efforts and a dramatic increase in the number of insurgents killed and captured by NATO, Afghan civilians faced growing danger.
"To the Afghan people, the credibility and value of a peace-negotiation process and progress toward peace will be measured by reduced civilian casualties and improvements in security," said Georgette Gagnon, director of human rights for the U.N. office in Kabul who led the team that produced the report.
"Only through increased actions to protect civilians will the relentless toll of death and injury to Afghan children, women and men be ended during and following a peace process."
The report also found 185,000 Afghans had been displaced in 2011, many of them fleeing conflict, up 45 percent from 2010 to the highest level in five years.