The New York Times reports as many as 13 people were killed on one of Afghanistan’s most important roads early Tuesday morning when gunmen opened fire on a bus and two other vehicles, the authorities here said. The episode is the latest in a series of attacks on the highway connecting Kabul with the southern city of Kandahar, and a grim reminder of the dangers of road travel across Afghanistan. The attack, around 1 a.m. on Tuesday, occurred southwest of Kabul, in Wardak Province, where the Taliban have a strong presence. Gunmen opened fire on a bus, as well as on two trucks, killing 12 men and a woman, said Attaullah Khogyani, a spokesman for the provincial governor. A Taliban spokesman, Zabihullah Mujahid, said that the attackers were not connected to the Taliban.