The death toll from a collision between a bus carrying Afghan migrants returning from Iran and two other vehicles in western Afghanistan has risen to 76, a provincial official said on Wednesday.

"Seventy-six citizens of the country... lost their lives in the incident, and three others were seriously injured," Mohammad Yousuf Saeedi, Herat provincial government spokesman, said in a statement.

The bus was carrying Afghans recently returned from Iran to the capital Kabul, Saeedi told AFP on Tuesday.

At least 1.5 million people have returned to Afghanistan since the start of this year from Iran and Pakistan, both of which have sought to force migrants out after decades of hosting them, according to the UN migration agency.

The state-run Bakhtar News Agency said on Tuesday that the accident was one of the deadliest in the country in recent years.

Traffic accidents are frequent in Afghanistan, attributed to decades of war-damaged roads, reckless driving on highways, and inadequate enforcement of regulations.

In December last year, two bus accidents involving a fuel tanker and a truck on a highway through central Afghanistan killed at least 52 people.