The United Nations says the number of civilians killed in the war in Afghanistan in the first half of this year rose 15 percent over the same period a year ago.

The U.N. mission in Afghanistan said Thursday more than 1,400 civilians had been killed, and attributed 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 United Nations said that while the overall number of civilians deaths linked to the U.S.-led NATO coalition fell by 9 percent, there was an increase in the number of those killed by air strikes.

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.