The number of civilians killed in the war in Afghanistan increased by 40% last year to a record 2,118 people, the UN said in a report today.

The research also showed 829 people were killed by US, Nato and Afghan forces, an increase of more than 30% year-on-year. Militants were responsible for 1,160 deaths, or 55% of the total, it said.

Campaign groups claim that 2008 marked the deadliest year in Afghanistan since the Taliban were deposed, and that ordinary Afghans have paid far too high a price.

Civilian deaths have been a huge source of friction between the US and the ­Afghan president, Hamid Karzai, who has demanded western troops avoid killing civilians during operations.

The US and Afghan militaries announced plans this month to increase the number of Afghans taking part in US operations, a step aimed at reducing civilian deaths.

The UN's annual report on the protection of civilians noted that despite new battlefield rules designed to reduce civilian casualties, western and Afghan troops killed 31% more civilians in 2008 than in 2007 – the UN claims 629 civilians were killed by Nato and Afghan forces.

"As the conflict has intensified, it is taking an increasingly heavy toll on civilians," the UN said.

Militants increasingly rely on roadside bombs, car bombs and suicide bombers – attacks that are "frequently undertaken regardless of the impact on civilians", the report said.

But US, Nato and Afghan operations also have led to rise in civilian casualties, "notwithstanding efforts to implement policies and procedures to minimise the impact of their operations on civilians", the report said.

About 130 deaths could not be accounted for because of issues such as crossfire.

A US-based group that pushes for the rights of civilians in conflict zones said in a new report today that "the lack of a clear, coordinated strategy to address civilian losses has been a leading source of anger and resentment towards military forces" in Afghanistan.

"The international coalition in Afghanistan is losing public support, one fallen ­civilian at a time," Civic (The Campaign for Innocent Victims in Conflict), said.

The US military and other members of the Nato-led force in Afghanistan make some condolence payments to the families of civilians accidentally killed. But Civic said that a "significant number" of families receive no help from international forces and that anger is especially strong when no help is provided.

"Every family with losses not recognised and addressed is another obstacle to Afghanistan's stabilisation and development," the report said.

The Civic report urged the Pentagon to create a position to address civilian casualties, and it said the Nato-led force in Afghanistan should have a coordinated response to provide compensation payments to the families of victims.