At least 25 people have been killed and 26 injured in Bolivia when the bus they were travelling in plunged into a ravine after colliding with a pick-up truck, investigators said.

The crash on Monday was the second in days in the southern Potosi department to claim dozens of lives - and the third in just a month.

On Saturday, at least 37 people died when a bus heading to the Oruro Carnival, one of the biggest festivals in Latin America, collided with another bus near the city of Uyuni.

Monday's accident took place around 90 kilometres (60 miles) north of the city of Potosi and also involved Oruro festival-goers -- this time people leaving the Andean city after the weekend carnival.

Investigators said they suspected the driver of the truck of causing the collision by crossing lanes into oncoming traffic, ramming headlong with the bus.

The pickup driver was taken into custody in hospital, where he was being treated for his injuries, police spokesman Limberth Choque told AFP.

The public prosecutor's office said he was being investigated for possible homicide and causing serious injury.

Drunk driving

The driver of one of the buses involved in the weekend crash had been drinking and was speeding when he veered into oncoming traffic, prosecutors said.

Six foreigners were among those killed: five Peruvians and a three-year-old German girl.

Horrific smashes are all too frequent on Bolivia's roads.

Road accidents kill an average of 1,400 people every year in the country of about 12 million inhabitants, according to government data.

Potosi accounts for 10.6 percent of all traffic accidents with fatalities in the South American country, according to the Bolivian Observatory of Citizen Security.

On February 17, at least 30 people died after a bus plunged into an 800-meter-deep abyss on the outskirts of Potosi.

The authorities said they suspected speeding as the cause of that crash.

In January, 19 people were killed when a bus careened off a road, also near Potosi.