KABUL (Reuters) - The United Nations on Monday called on insurgent groups in Afghanistan to curb attacks on civilians after more than 5,000 non-combatants were killed or wounded in the first six months of 2017.

FILE PHOTO: Damaged vehicles are seen after a suicide car bomb attack in Khost province, Afghanistan May 27, 2017. REUTERS/Stringer

The war in Afghanistan killed at least 1,662 civilians and wounded 3,581 in the first half of the year, roughly similar to the toll in the same period in 2016, U.N. investigators said in a statement released on Monday.

Deaths and injuries from suicide-bombings and other “complex attacks” rose 15 percent, with at least 40 percent of all civilian casualties caused by anti-government groups using improvised explosives, including along roadsides.

“The human cost of this ugly war in Afghanistan – loss of life, destruction and immense suffering – is far too high,” Tadamichi Yamamoto, the head of the U.N. Assistance Mission in Afghanistan, said in a statement.

“The continued use of indiscriminate, disproportionate and illegal improvised explosive devices is particularly appalling and must immediately stop.”

In May, a massive truck bomb in the heart of the capital, Kabul, detonated by a suicide attacker, killed at least 92 people and wounding nearly 500 in what the United Nations called the “deadliest incident documented” since the international military intervention that toppled the Taliban regime in 2001.

No group claimed responsibility for the attack.

Kabul has accounted for nearly 20 percent of all civilian casualties this year.

The investigators said the Taliban were responsible for at least 43 percent of all civilian casualties. Islamic State was blamed for 5 percent, while unidentified anti-government forces accounted for another 19 percent of the total.

Taliban spokesman Zabihullah Mujahid called the U.N. findings politically motivated “propaganda material”.

“We once again strongly reject this report,” he said in a statement.

“The Islamic Emirate is much more sensitive to and vigilant about prevention of civilian casualties than any other side,” he added, using the official name of the Taliban.

The investigators praised Western-backed Afghan police and soldiers, with civilian casualties caused by them 21 percent lower this year.

Deaths and injuries from air strikes, however, spiked 43 percent, as both Afghan and U.S. forces increased their air operations.

At least 95 people were killed and 137 wounded in air strikes, the investigators said.

Among those hardest hit in the violence this year were children, with child deaths increasing by nine percent.

“These civilian attacks need to stop,” said David Skinner, country director for the aid group Save the Children.

“Not only do they injure and kill innocent people in the most horrific way, but they cause untold distress and trauma, especially for children, often leading to serious psychosocial issues and impacting their longer term development.”