KABUL: Up to 35 people were killed in a fireball Wednesday when a bus carrying passengers taking home gas canisters collided with a truck on a treacherous mountain pass in northern Afghanistan.

The bus was travelling north from Kabul along the narrow Salang pass when it "had an accident with a truck, as a result of which 35 passengers, including women, men and children, were killed," the interior ministry said.

The Salang pass -- the fastest route connecting northern and southern Afghanistan -- is a notoriously dangerous stretch of road, and the scene of avalanches in February that killed 170 people.

Police said initially that the bus crashed into an oil tanker, but the spokesman for the northern regional police, Lal Mohammad Ahmadzai, said the bus passengers were returning from Iran carrying canisters of gas.

"The bus was bringing families home from Iran and many of them had bought gas in Iran because it is cheaper there. So when the bus slammed into the truck, the canisters exploded," he told AFP.

Afghan homes generally use gas canisters to fuel stoves for cooking.

The interior ministry said the accident appeared to have been caused by the "narrow width of the road" and driver "carelessness".

"In the first moments after the incident police and first aid health workers arrived on the site and transferred a number of people to the provincial hospital," it said.

It did not give details of the number of injured.

President Hamid Karzai offered his condolences to the families of the dead.

The accident happened when the truck driver lost control of his vehicle and smashed into the bus, Karzai's office said.

It put the number of dead at 32, with six injured.

The type of bus involved in the crash can accommodate more than 50 passengers, a former bus driver said.

In February, the Salang pass was closed for four days as rescue workers dug through heavy snow and ice to recover bodies after avalanches in one of the country's worst natural disasters.

One of the highest highways in the world at around 3,650 metres (12,000 feet), the pass includes a 2.6-kilometre tunnel and was hailed as an engineering feat after it was completed with Soviet help in the 1950s.

Due to its relative isolation, much of northern Afghanistan has been somewhat sheltered from the eight-year Taliban insurgency that more than 120,000 NATO and US troops are trying to quell.

Traffic on the Salang pass is building as Afghans prepare to celebrate the Nowruz new year, which falls on March 21.

Many people travel to the northern provinces to spend the national holiday in one of the most peaceful regions of the war-wracked country.