The violence that started on Sunday and lasted into the early hours of Monday outside the Parliament in central Beirut came on the eve of talks the Lebanese President Michel Aoun was expected to hold with parliamentary blocs to name a new premier, reports Efe news.
The Lebanese Civil Defence said on Twitter that they had transferred those "20 injured to hospitals in the region to receive medical attention", adding that at least 72 others, including a photographer, were treated on the ground.
Meanwhile, the Lebanese Red Cross added it transported four injured in the clashes that broke out when the forces fired teargas and water cannons to disperse demonstrators, who started hurling fireworks.
Local media outlets identified those who triggered the clashes as supporters of the Shiite movements Hezbollah and Amal.
The Lebanese security forces released live footage showing "infiltrators" in the protester ranks "provoking the troops before the dispersion started".
On December 14, dozens of people were injured in a similar situation, to which the security forces had responded with using "excessive violence" against protesters.
Raya al-Hassan, the Lebanese Interior Minister, has ordered an investigation into the clashes.
Lebanon has been gripped by street protests since October 17, prompting the previous Prime Minister Saad Hariri to resign after 12 days on October 29.
According to the Lebanese constitution, the premier must always be a Sunni Muslim, while the presidency is reserved for a Christian Maronite and the speakership of the lower house is occupied by a Shia Muslim, according to the power-sharing deal between the three main religious sects.
( With inputs from IANS )