MAZAR-I-SHARIF, Afghanistan (AFP) — A roadside bomb killed seven petroleum company employees aboard a bus in northern Afghanistan on Tuesday, a provincial police spokesperson said.

"The bomb was placed in a cart by the roadside. It was detonated as the bus arrived," Asif Waziri, of the Balkh police department in Mazar-i-Sharif, said.

Although the Taliban claim to have improved security across the nation since storming back to power in August last year, there have been scores of bomb blasts and attacks — many claimed by the local chapter of the Islamic State group.

At least 19 people were killed and 24 others wounded earlier this month by a blast at a madrassa in Aybak, southeast of Mazar-i-Sharif.

Waziri told AFP Tuesday's blast happened around 7:00 a.m. near Sayed Abad Square in the city.

He said six people were injured in the blast.

Further details were not immediately available, and there has been no claim of responsibility.