KABUL, Afghanistan  — Three U.S. soldiers were killed in Afghanistan's eastern borderlands on Sunday, U.S. and NATO officials said, the first NATO combat deaths this month.

The soldiers, from the NATO-led International Security Assistance Force (ISAF), were killed by insurgents in Paktia province, a U.S. official told Reuters.

The last NATO soldier to be killed in action was late last month.

Paktia is one of several provinces that border Pakistan and have endured some of the highest levels of fighting during the U.S.-led 12-year war in Afghanistan.

U.S. soldiers based in Paktia are rarely involved in combat operations since handing over security responsibility to Afghan security forces earlier this year. They now primarily train their Afghan colleagues.

The NATO-led mission has about 100,000 international troops in Afghanistan, of which about 68,000 are American. Those numbers are expected to reduce sharply before the official end of the NATO-led combat mission - Dec. 31, 2014.

More than 2,100 U.S. soldiers have died during the war in Afghanistan.