The dead were employees of a petroleum company aboard a bus in Mazar-i-Sharif, a local official said.
At least seven people have been killed in a roadside explosion in northern Afghanistan, local officials said.
Those killed in Tuesday’s 07:00 (03:00 GMT) blast in the town of Mazar-i-Sharif included employees of a petroleum company on a bus, local officials said.
“The bomb was placed in a cart by the side of the road. It exploded when the bus arrived,” said Asif Waziri of Balkh police in Mazar-i-Sharif.
The northern province of Balkh contains one of the country’s most important dry ports in the town of Hairatan near the border with Uzbekistan, with rail and road links to Central Asia.
It was not immediately clear who was behind the attack, which comes amid repeated pledges by the Taliban government to bring security to Afghanistan after decades of war.
The Taliban government came to power in August last year after a withdrawal by US-led foreign forces that invaded the country and ousted the group from power in 2001.
Last month, at least 19 people were killed and 24 others injured in a blast at a school in Aybak, a town in Samangan province bordering Balkh province.
In May, at least nine people were killed in a series of explosions in Mazar-i-Sharif, while two others were killed in a simultaneous attack on a mosque in the capital, Kabul.
ISIL (ISIS) – the Taliban’s main rival in Afghanistan – had claimed responsibility for the attack in Mazar-i-Sharif, but not for the attack in Kabul.
Recent violence also included a suicide bombing that killed four near a mosque in the Afghan Ministry of Interior building complex in October.