The Army in Lebanon says the country is going through a critical time and the level of tension in some areas is high.
A senior security official was assassinated in Beirut on Friday.
Protesters set up road blocks in Beirut on Sunday night after the funeral of General Wissam al-Hassan and exchanges of gunfire were reported.
Troops backed by armoured personnel carriers were sent into the streets on Monday morning to restore calm and re-open the roads.
In a statement issued on Monday, the Army said the last few hours "have proven without a doubt that the country is going through a decisive and critical time and the level of tension in some regions is rising to unprecedented levels".
It urged "all political leaders to be cautious when expressing their stances and opinions" and in attempting to mobilise public action "because the fate of the nation is at stake".