The U.N. Assistance Mission in Afghanistan says one of its staff members was killed Tuesday in an attack in the capital, Kabul.

The U.N. said one of its vehicles carrying two Afghan workers came under fire at a busy traffic circle in Kabul.  The other employee was unharmed.

U.N. mission condemned violence against "any of its personnel under any circumstances" and said the motive for the shooting is unclear.

On the outskirts of Kabul, a protest against NATO forces turned violent Tuesday, with at least 20 people injured in clashes with police.

Demonstrators took to the streets to protest what residents say was a NATO raid on a local religious school (madrassa) late Monday, arresting a number of people.

But Afghan police officials said only Afghan security personnel were involved in the operation.

In other violence Tuesday, a roadside bomb killed two civilians in southern Kandahar province, while an insurgent attack killed six security guards in neighboring Zabul province.

In northeastern Kunar province, an Afghan-led joint force battled hundreds of insurgents for a third day. The militants are believed to be responsible for the June 7 roadside bombing that killed five U.S. troops.

On Wednesday, NATO marks one year since Taliban insurgents captured U.S. soldier Bowe Bergdahl in eastern Paktika province.  The group later released videos of Specialist Bergdahl, demanding the release of prisoners in exchange for his freedom.

The military says finding Bergdahl and bringing him home safely is a top priority for U.S. and NATO forces.

Some information for this report was provided by AP.