The official handover of responsibility for security in Afghanistan from Nato to local forces has been marked by a deadly blast. The explosion in the west of Kabul killed three people and injured 30.

Officials said a suicide bomber targeted Mohammed Mohaqiq, a prominent Hazara policymaker in the region and Afghanistan's second vice-president.

"The roadside bomb targeted the Mohaqiq convoy but he safely passed. One of his vehicles was damaged," said chief of Kabul police, Gen Mohammed Zahir.

Scores of Nato and local officials had gathered to mark the official handover - a significant milestone 12 years after a Nato coalition went in to Afghanistan to expel the Taliban in the wake of the 9/11 attacks.

Under the terms of the handover, the 100,000 Nato troops stationed in Afghanistan will play an increasingly peripheral role in national security until their formal departure in 18 months.

President Hamid Karzai announced the transition during a ceremony but critics are mixed about the readiness of Afghan security forces.

"Our security and defence forces will now be in the lead. From here, all security responsibility and all security leadership will be taken by our brave forces," Karzai said.

The last districts to be handed over to Afghan forces include some of the most volatile in the country.

The Taliban insurgency has been intensifying after the militant group declared a spring offensive.

According to UN figures, more than 3,000 civilians were killed between January and June this year, a sharp increase from the 2012 count.