KABUL, Sept 18 (Reuters) - A NATO force was ambushed by insurgents on Thursday in eastern Afghanistan and suffered some casualties, an alliance spokeswoman said.

The ambush in Kunar came hours after a soldier of NATO's International Security Assistance Force (ISAF) died in a separate attack of the insurgents in another area of the province which borders Pakistan, she said.

Violence has surged to its worst level in Afghanistan this year, the bloodiest period since U.S.-led troops overthrew the Taliban government in 2001.

Despite an increase in strength of foreign troops, now numbering more than 71,000, the al Qaeda-back Taliban have not only been intensifying their guerrilla attacks, but extending the scope of their activities.

Thursday's ambush came a day after four U.S. soldiers and an Afghan national were killed in a roadside bomb on a highway in a southeastern area.

At least 195 foreign troops have been killed so far in 2008 in Afghanistan. (Reporting by Sayed Salahuddin; Editing by Jerry Norton)

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