Kabul, Afghanistan (CNN) -- At least 14 family members heading to a engagement party in western Afghanistan were killed when a minibus struck a roadside bomb, a local official said.

The incident took place in Herat province, which has not been regularly engulfed in the brutal warfare seen in other regions -- such as the east and the south.

The bus was headed from Kosh-e-Kohna district to the city of Herat when it struck the explosive, said Shafiq Behrazian, spokesman for the Herat provincial governor.

Four people were injured, and the casualties included women and children.

Koshk-e-Kohna is a remote district in the northern part of the province, and there is only one small road -- also used by NATO and Afghan forces.

Behrazian said it was unclear if coalition forces were the targets of the bombing. He said an investigation has been launched.

In Helmand province, NATO-led forces are probing a Wednesday airstrike that reportedly killed four Afghan National Army soldiers.

The incident occurred after an Afghan and coalition patrol came under small arms fire from insurgents.

The troops called in air support and an aircraft "positively identified the insurgent firing position and conducted an airstrike," NATO's International Security Assistance Force said.

Daud Ahmadi, spokesman for the Helmand governor, confirmed the airstrike and the deaths, and he said the people were killed by mistake.