At least seven people were killed in Afghanistan on Tuesday when an explosion struck a vehicle carrying oil workers in the northern province of Balkh, and a second explosion injured six people in the eastern city of Jalalabad.

"Today at approximately 7:00 a.m., an explosion occurred on a Hairatan oil workers bus in Balkh," said Mohammad Asif Wazeri, a police spokeswoman for the northern province.

He stated that at least six persons were injured.

Balkh province contains one of Afghanistan's most important dry ports in the town of Hairatan, close to the border with Uzbekistan and with train and road connections to Central Asia.

Wazeri stated that Balkh police were searching for those responsible for the vehicle explosion. It was unclear who the bus's employees worked for.

According to officials in Nangahar province, a second explosion near the money exchange market in Jalalabad injured six persons later in the day.

The causes of the explosions were not immediately discernible.