The number of children killed or wounded in Afghanistan's conflict surged in the first half of 2016, compared to the same period last year, the United Nations mission in Afghanistan said on Monday.

The daunting figures came in a mid-year report by UNAMA, released just days after the deadliest bombing to hit Kabul since the insurgency began in 2001, following the U.S. invasion to topple the Taliban's brutal regime.

On Saturday, at least 80 people were killed and 231 wounded in a suicide attack on a peaceful demonstration of the Afghan minority Shiite Hazara community. Most of those killed were civilians.

The Islamic State group claimed responsibility, fuelling concerns that the extremists, who have had a presence in the remote eastern border regions near Pakistan for the past year, plan to raise their profile in Afghanistan as they rack up losses in their heartland in Iraq and Syria.

The figures from Saturday's attack are not part of UNAMA's report, which documents casualties between Jan. 1 and June 30 this year.

The report says that one-third of the casualties during those six months were children, with 388 killed and 1,121 wounded. That's 18 per cent more than during the first half of 2015.

Ahmad Shuja, Afghanistan researcher for New York-based Human Rights Watch, attributed the alarming rise in the number of deaths and injuries to children to a changing landscape of war.

Whereas the Taliban previously relied on hit-and-run tactics and the use of remotely-detonated explosives, now they engage in ground battles with government troops, and often deliberately target schools, community centres and civilian homes, Shuja told The Associated Press.

Shuja, whose HRW was not involved in the UNAMA report but has done its own reports on children in conflict, said the New York-based watchdog found that Afghan security forces are also "often responsible for badly aimed artillery and mortar fire," contributing to the casualties.

While 2015 saw the highest number of civilian casualties since 2009, when UNAMA started collating civilian casualties, numbers for this half-year were similar to last year.

UNAMA documented 5,166 civilian casualties — 1,601 killed and 3,565 wounded — marking a one per cent fall in civilian deaths and a six per cent rise in the number of wounded civilians.

Total civilian casualties were up four per cent, compared to the first half of last year, the report says.

That's similar to the figures from the previous year, which was particularly bad as Afghan forces took the lead in fighting following the 2014 withdrawal of most international combat troops.

More than 20,000 killed

Overall, UNAMA's report says that from Jan. 1, 2009 until June 30, 2016, a total of 63,934 civilian casualties — 22,941 deaths and 40,993 wounded — have been recorded.

"Anti-government elements" were responsible for 60 per cent of civilian casualties, UNAMA says, but notes "an increase in the number of civilians killed and injured by pro-government forces.

In the first half of this year, UNAMA documented 1,180 civilian casualties attributable to pro-government forces, or 23 per cent of the total. However, it said this was a 47 per cent increase compared to the same period last year, primarily as a result of stepped-up battles across the country.

"Ground engagements continue to cause the highest number of civilian casualties, followed by complex and suicide attacks and improved explosive devices," the report says.

"Explosive remnants of war disproportionately impacted children who comprised 85 per cent of the casualties caused by such devices," it says. Afghanistan remains one of the most heavily mined countries in the world, after almost 40 years of conflict.

UNAMA also says that during the first half of this year, it recorded 157,987 "newly displaced" people, a 10 per cent increase of the same period last year, bringing the total estimate of people displaced by conflict to 1.2 million.