KABUL — Suspected Taliban gunmen ambushed Afghan guards who were in a vehicle headed to work at the U.S.-run Bagram air base, killing at least eight people as part of a surge of attacks by militants around the country, officials said Tuesday.

A Taliban spokesman, Zabiullah Mujahid, said the group carried out the late Monday assault and described the victims as spies for the U.S. military.

Attacks by the Taliban and its Islamic State rivals have been rising in Afghanistan as the United States completes plans to send several thousand more troops to bolster Afghan forces and the 8,500 U.S. troops already in the country.

“We cannot rule out anything — enemy attack, local or tribal hostility,” provincial Police Chief Mohammad Zaman Mamozai said by phone in reference to the attack on the Bagram guards. He said two other occupants of the vehicle suffered bullet wounds.

Meanwhile, violence flared in a series of attacks around the country and in the capital, Kabul, between security forces and protesters who had occupied a busy avenue for the past three weeks.