NATO has said four of its service members died Thursday in three separate incidents in southern Afghanistan.

A NATO statement said three soldiers were killed by two bomb blasts, while the fourth died in an insurgent attack.

More than 390 international troops have been killed in Afghanistan so far this year.

Taliban insurgents are increasingly using improvised explosive devices to target both security forces and Afghan civilians.

In a report last month, the United Nations 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.