A bomb hidden in a parked minibus has exploded outside a government building in southern Afghanistan, killing two Afghan intelligence officers, authorities said.

Monday's attack targeted a field office of the Afghan intelligence agency, the National Directorate of Security, in the city of Lashkar Gah in Helmand province, said Ahmed Zarak, a spokesman for the provincial government.

He added that at least 15 people were wounded in the blast, most of them civilians who lived in a house next door.

It was not clear whether the explosives were remotely detonated or fixed to a timer, he added.

The two officers who were killed were guarding the compound, which the NDS uses as a base for operations inside Laskgar Gah, the provincial capital, Zarak said.

The number of casualties among Afghan security forces has been on the rise as Afghan troops have shifted into a more frontline role in the war against the Taliban and other insurgent groups as international forces draw down in number.

Civilians have also continued to suffer heavy casualties from bombings and targeted killings.

The outgoing head of the International Red Cross mission in Afghanistan told reporters on Monday that civilians are in greater danger with less hope for peace than when he took up his post seven years ago.

"As the armed conflict in Afghanistan rages on, life for ordinary Afghans has taken a turn for the worse," said Reto Stocker as he prepared to leave the job he has held since 2005.

Stocker said the proliferation of armed groups in the country has continued to make it difficult for the Red Cross to operate and for civilians to seek medical attention when they are caught up in the violence.

Monday's violence came as the International Crisis Group released a report painting a gloomy prediction of Afghanistan's future.

The report said the Afghan government could implode after NATO troops pull out in 2014, particularly if presidential elections are fraudulent.