The Lebanese army is determined to restore order across the country, military command said on Monday, as violence hit parts of the capital and the northern port of Tripoli and troops came under fire.

The army is "committed to its role of stopping security breaches and maintaining civil order," a statement said.

"Recent developments prove decidedly that the country is going through a critical time, and the level of tension in some areas has reached unprecedented levels," it said.

The army will take "resolute measures, particularly in areas of mounting sectarian friction... to prevent the assassination of martyred General Wissam al-Hassan from being exploited as an opportunity to murder the nation as a whole."

Hassan died in a car bomb attack on Friday widely blamed on Syria, and his death has prompted much of the violence since then.

The army stressed that "security is truly a red line, not only in words, as is the targeting of official institutions and infringement on the sanctity of public and private property."

It called on "citizens from all backgrounds and affiliations across Lebanon to exercise the highest degree of civic responsibility in these difficult times, and not let their emotions control the situation."

It added that demonstrators must leave any roads that were cut off.

The military command appealed to all political forces to be wary with their words and calls for mobilisation, "because the fate of the nation is at stake."