Live rounds and rubber bullets were fired by Lebanese soldiers as anti-government protesters tried to march on the presidential palace.
Supporters of President Michel Aoun gathered at the same location for a counter-protest.
Tension is high in Lebanon after last month’s devastating explosion at Beirut’s port, which killed at least 191 people, and another huge blaze at the same site on Thursday.
The blast on August 4 was caused by nearly 3,000 tonnes of ammonium nitrate which had been improperly stored at the port for years.
More than five weeks later, it is still not clear what ignited the chemicals, and no one has been held accountable so far.
Anti-government protesters wanted Saturday’s march to the presidential palace in the suburb of Baabda to be a call for accountability.
Hundreds of Lebanese soldiers separated the two camps.
Later, as anti-Aoun protesters tried to break a security cordon blocking their path on the main road leading to the palace, troops fired live rounds in the air, then rubber bullets, to disperse them.
Some protesters threw stones and branches at the troops, injuring several of them. Others sat in the middle of the street, vowing to stay there. A group climbed on a signpost and hung ropes tied into nooses.
The Lebanese army has been clearing the Beirut port wreckage for weeks.
A World Bank report estimated the damage to Lebanon’s transport sector and port alone to be between $580 million (Dh2.13billion) and $710 million.
Several countries have already signalled their interest in reconstruction.
Kuwait was the first to come forward, and France has sent hundreds of soldiers to the city.