Ashraf Ghani

President Ashraf Ghani said the assault near the northern city of Mazar-e-Sharif had been contrary to all human values and Islamic teachings.

Insurgents targeted those leaving Friday prayers at the base's mosque and others in a canteen, the army said.

Some of the survivors suggested the attackers had had inside help.

One of the injured soldiers said: "When an attacker enters the base, why was he not challenged? There is not just one barrier or security gate, there are seven or eight."

Munir Ahmad Farhad, the spokesman for the governor of Balkh province, said the civilians were killed by unidentified gunmen who stopped their vehicles and then shot them dead.

The incident took place as Ghani opened a conference of donors to his country's reconstruction after almost 40 years of war, telling them he has made progress on a range of major challenges including security and corruption.

The attack sends the strongest message yet to Afghan President Ashraf Ghani — that militants are still able to strike at his heavily fortified seat of power.

No one claimed responsibility for the attacks, though officials indicated they blamed the Taliban.

The Afghan president, Ashraf Ghani, expressed his "profound sorrow" over the tragedy and ordered an investigation into the killings.

The incident happened as coalition helicopters were flying over an area in Logar province where clashes were underway between Afghan troops and Taliban fighters, the Afghan Ministry of Defense said.