Afghan officials say a roadside bomb has killed five civilians in southern Afghanistan.

Authorities say the civilians were killed Friday when their vehicle hit a landmine in the Sangin district of Helmand province. At least one person was wounded.

The deaths came a day after the United Nations reported that the number of civilians killed in Afghanistan has gone up by 15 percent in the first six months of this year compared to same period last year.

The U.N. mission in Afghanistan said Thursday that more than 1,400 civilians were killed between January and the end of June, attributing the deaths to increased ground fighting, roadside bombs, suicide attacks and a rise in NATO airstrikes.

The U.N. said roadside bombs were the single-largest killer of civilians in the first half of this year.

Meanwhile in Kabul, Afghan President Hamid Karzai took part in a memorial service for his assassinated half-brother at his palace Friday. Top Afghan and Western officials were in attendance.

Ahmad Wali Karzai was chief of the Kandahar provincial council and a powerful figure in the country's south. He was shot dead Tuesday at his home in Kandahar city by a trusted longtime member of his own security team.

The Taliban claimed responsibility for the assassination. But Afghan officials said it is not clear whether Wali Karzai's killing was related to the insurgency or to an internal feud.