Afghan officials say six civilians have been killed during a NATO operation in eastern Afghanistan, as the United Nations reported that the number of Afghans killed in the war is up 15 percent this year compared to last.

Hundreds of residents demonstrated Thursday in the city of Khost, where local officials said six civilians, including a teacher and a young child, were killed in an overnight coalition raid.

NATO said an Afghan-led security force killed six Haqqani-network militants during the security operation in Khost district late Wednesday. The coalition said militants, including a female insurgent, fired on the joint force while troops worked to clear a compound. NATO says one female civilian received non-life threatening injuries.

But Afghan officials said Thursday that the coalition received an incorrect report and that all of those killed during the security operation in Khost district were civilians.

Meanwhile, the U.N. mission in Afghanistan said Thursday that more than 1,400 civilians were killed in the first six months of this year, attributing the deaths to increased ground fighting, roadside bombs, suicide attacks and a rise in NATO air strikes.

The report blamed insurgents for 80 percent of civilian deaths, and said foreign and government forces were responsible for 14 percent of the killings.

The U.N. special representative in Afghanistan, Staffan de Mistura, said Thursday the U.N. mission has been in touch with the Taliban to try and get the insurgent group to reduce civilian casualties.

The United Nations says that while the overall number of civilian deaths linked to the U.S.-led NATO coalition fell by nine percent, there was an increase in the number of those killed in airstrikes, mainly carried out by Apache attack helicopters.

The report also said the number of deaths from roadside bombs increased by 17 percent this year compared to the same period in 2010, making them the single-largest killer of civilians in the first half of this year.

The U.N. says the number of targeted killings the first half of this year rose to 190 compared to 181 during the same period last year.

Violence in Afghanistan has hit the worst levels since the U.S.-led invasion in 2001, and May was the deadliest month for Afghan civilians since the United Nations mission began compiling statistics four years ago.