Hezbollah, Amal supporters attack main Beirut protest camp
The men - who observers identified as "thugs" from Lebanon's two main Shia movements - are seen in videos circulating social media as shoving and beating other demonstrators on the Beirut Ring Road, which has been the epicentre of the roadblocks that have brought the country to a virtual standstill for almost two weeks.
Despite the army being present at the demonstrations, officers captured on video seemed unable to stop the violence.
Supporters of Hezbollah and Amal have previously attacked demonstrators in the capital and the southern city of Nabatieh, a Shia stronghold.
On Friday, clashes erupted when partisans of the powerful Iranian-backed Shia group entered Beirut's Riad Al-Solh square, chanting in support of Hezbollah threatening and intimidating protesters against voicing any criticism of their leader Hassan Nasrallah.
Friday's clashes hospitalised at least six people, a rare show of violence amid the otherwise peaceful protest movement demanding an end to corruption, economic problems and political stagnasis.