Police have used water cannons to break up a protest by relatives of several kidnapped Lebanese soldiers, after the protesters blocked a main highway in the capital.

Several protesters and some journalists were also beaten by security forces as they broke up the demonstration.

The Islamic State group and al-Qaida-linked Nusra Front in Syria seized some 20 Lebanese soldiers and police officers in August during a brief cross-border raid. They have already killed three of the captives, beheading two.

Friday's protest came a day after Nusra Front threatened to kill one of the soldiers. The families are demanding that the government negotiate seriously with the militants — who are demanding the release of Islamist prisoners from Lebanese jails.

Lebanon's Interior Minister Nohad Machnouk said blocking roads "is not the answer."