MAZAR-I-SHARIF, Afghanistan: A bomb attack Wednesday killed four people and wounded 11 others in the Afghan city of Mazar-i-Sharif, due to transition from foreign to local control this week, police said.

Local police Chief Abdul Rauf Taj said explosives carried by a man with a bicycle in the Dasht-i-Shor area of the northern city detonated, but it was not yet clear if the man was a suicide bomber.

“The explosives detonated and killed four people and injured 11 other people. They were all civilians,” said Taj. “We're investigating.”

Mazar-i-Sharif is one of seven areas to transition from foreign forces to Afghan control this week, as Nato-led troops begin a gradual withdrawal designed to recall all its combat troops by the end of 2014.

The city was thrown into turmoil in April when demonstrators, protesting at the burning of a Koran by a US pastor, attacked a UN compound and killed seven foreign staff.

Government officials said the demonstration had been infiltrated by insurgents.