UN Special Representative for Afghanistan, Tadamichi Yamamoto, says, "When we document these appalling civilian casualty figures, it hurts, because it counters the best interests of this country and undermines efforts serving the people of Afghanistan".
The United Nations Assistance Mission in Afghanistan (UNAMA) reported that civilian deaths across the country fell nine percent overall in 2017, with 10,453 casualties including 3,438 deaths and 7,015 wounded.
U.S. President Donald Trump introduced a more aggressive U.S. strategy in Afghanistan in August including a surge in air strikes.
Pro-government forces caused a fifth of civilian casualties with 16 percent attributed to Afghan forces, 2 per cent to worldwide forces and 1 percent each to pro-government armed groups and undetermined pro-government forces, the United Nations said.
The use of improvised explosive devices (IEDs) - suicide and non-suicide - by armed groups led to the majority of the casualties a year ago, with ground engagements accounting for the second-highest number of victims.
Yamamoto, who also heads UNAMA, expressed deep concern at the increased harm to civilians caused by suicide attacks: "I am particularly appalled by the continued indiscriminate and unlawful use of IEDs, such as suicide bombs and pressure-plate devices in civilian populated areas".
Eleven percent of the civilian casualties in 2017 were caused by unaccounted fire between Afghan troops and anti-government fighters.
Islamic State militants are responsible for a large number of these attacks, especially on Shia mosques.
"Pro-government forces, which include Afghan National Security Forces, worldwide military forces and pro-government armed groups were responsible for 20 percent of civilian casualties", Bell said.
"Such attacks are prohibited under global humanitarian law and are likely, in most cases, to constitute war crimes".
Afghan President Mohammad Ashraf Ghani said during a press conference on Sunday that the Taliban-claimed January 27 attack near a public hospital, in which over 100 people got killed, was "Afghanistan's 9/11".
It attributes 16 per cent to Afghan forces and 2 per cent to worldwide forces, with the rest remaining unclear.
"2017 recorded the highest number of civilian casualties from suicide and complex attacks in a single year in Afghanistan", the report said, with 605 killed and 1,690 wounded from such incidents.
The casualties by pro-government forces were mainly caused by the increase in aerial bombings by Afghan and foreign forces, the UNAMA said.
That compares to a total 11,434 casualties in 2016, when there were 3,510 deaths and 7,924 wounded.