The guards, employees of a Houston company, were accompanying a company vehicle when they were hit by the roadside bomb in the town of Gereshk, CNN reported quoting the Afghan Defense Ministry.

No one claimed responsibility for the attack.

In a similar attack last December, Taliban militants killed 15 Afghan employees of the Houston firm after ambushing a convoy carrying fuel bound for U.S. military bases in western Afghanistan, the report said.

The latest incident comes in the wake of an attack Sunday at an outpost in eastern Afghanistan in which nine U.S. soldiers died, the deadliest such incident against U.S. troops in three years, the report said.

Afghan military officials said the incident in Dara-I-Pech in Kunar province near the border with Pakistan involved 400 to 500 militants.

He said at least 100 of the militants were also killed or injured.