KABUL: More than 10,000 Afghan civilians were killed or wounded in violence last year, the United Nations said on Thursday, with militant bombings the main cause while air strikes by US and government forces inflicted a rising toll.

US President Donald Trump introduced a more aggressive US strategy in Afghanistan in August including a surge in air strikes. The militants have responded with attacks in Kabul in the past few weeks, killing nearly 150 people.

The overall civilian toll last year of 3,438 killed and 7,015 wounded was 9 percent lower than the previous year. But the figures highlighted the high number of casualties caused by militant bombs, the United Nations said.

"Attacks where anti-government elements deliberately targeted civilians accounted for 27 per cent of the total civilian casualties ... mainly from suicide and complex attacks," the United Nations said in a statement.

The deadliest attack since the UN mission began recording civilian casualties in 2009 was in Kabul on May 31 when a suicide attacker detonated a truck bomb, killing 92 civilians and injuring 491.

Two-thirds of all casualties last year were inflicted by anti-government forces, with the Taliban responsible for 42 percent, Islamic State 10 percent and 13 percent caused by undetermined anti-government elements.

Pro-government forces caused a fifth of civilian casualties with 16 percent attributed to Afghan forces, 2 per cent to international forces and 1 percent each to pro-government armed groups and undetermined pro-government forces, the United Nations said.

The air campaign by international and government forces accounted for 6 percent of civilian casualties in 2017, with 295 people killed and 336 wounded, a 7 percent increase over the previous year.

While ground clashes were the second leading cause of civilian casualties, that toll was 19 percent lower than a record level seen in 2016.

Women and children were heavily affected by the violence with 359 women killed last year, an increase of 5 percent over the previous year - and 865 injured.

The number of child casualties - 861 killed and 2,318 wounded - was 10 percent lower than 2016.

"Afghan civilians have been killed going about their daily lives - travelling on a bus, praying in a mosque, simply walking past a building that was targeted," UN High Commissioner for Human Rights Zeid Ra'ad al Hussein said in a statement.

"Such attacks are prohibited under international humanitarian law and are likely, in most cases, to constitute war crimes. The perpetrators must be identified and held accountable."