KABUL, July 28 (Reuters) - Three NATO troops and an Afghan soldier have been killed in two separate clashes with insurgents in Afghanistan, the alliance said.

The identities of the NATO soldiers were not given.

Two of the NATO soldiers and the Afghan were killed on Friday in an area of eastern Nuristan province in a clash with Taliban rebels. Thirteen NATO soldiers were wounded in that incident.

The third NATO soldier was killed in another encounter in the south of the country, also on Friday. The alliance did not say if there were any casualties among the insurgents.

Violence has surged in Afghanistan in the past 18 months, the bloodiest period since Taliban's overthrow in 2001.

Friday's deaths brings the number of foreign troops killed in the country this year to more than 90.

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