At least four police officers were killed after a suicide bomber detonated a car laden with explosives next to a police convoy in Afghanistan's Helmand province, a spokesman for the local governor told Al Jazeera.

The convoy was targeted while traveling on the Herat-Kandahar highway, said Omar Zwak on Sunday, adding that eleven other officers were also injured in the blast.

Police spokesman Colonel Farid Ahmad Obaid confirmed the attack, which took place in Lashkargah, Helmand's provincial capital.

No group has claimed responsibility.

In a separate development, the country's National Directorate of Security (NDS) said on Sunday it had foiled a complex suicide attack on the Ministry of Interior's compound in Kabul.

Five would-be-attackers, including suicide bombers, were arrested said Afghan's intelligence agency.

Source: Al Jazeera